The Modern Bullpen: How Teams Are Reinventing Relief Pitching in the Analytics Era

Why dominant relievers aren’t what they used to be — and why that’s by design.

The Death of the Traditional Closer

In 2024, only four MLB pitchers recorded more than 30 saves. For perspective, that number was twelve just a decade ago, and over twenty in the early 2000s. The “closer” — once the fire-breathing dragon of the ninth inning, summoned by trumpet or Metallica riff — is rapidly becoming a relic.

The change hasn’t been gradual. It’s been seismic. Across Major League Baseball, teams are abandoning traditional bullpen roles in favor of leverage-based deployment. Matchups now trump innings. “Stuff” now trumps experience. And the fireman might enter the game in the 6th, not the 9th.

But this isn’t just about when relievers pitch — it’s about how they’re built, how they’re developed, and how front offices think about them. A new era has arrived, one shaped by biomechanics labs, spin-axis modeling, and ultra-specialized coaching.

Today, a reliever might get drafted not because of ERA, but because his vertical approach angle and induced vertical break make him un-hittable at the letters. His college stats might be irrelevant — if he throws 96 from a low slot with a whiff-heavy sweeper, he’s a priority.

So how did we get here? What exactly makes a modern bullpen successful? And how can coaches and player development departments adapt to this new paradigm?

Let’s break it down.

The Anatomy of the Modern Bullpen

Modern bullpens are no longer just a collection of failed starters and journeymen arms. They're engineered — piece by piece — to create specific matchup problems across a game’s most volatile innings. Velocity is just the starting point. What really defines a modern bullpen is pitch shape, release characteristics, and deception.

Let’s break down the common traits you’ll find across most elite relief units today:

🔹 Short Outings, Max Effort

In today’s game, relievers are expected to go all out — often for 15–20 pitches max. Starters may need to manage effort across five or six innings; relievers don’t. This means:

• Higher average velocity across the board (MLB bullpen avg FB: 95.6 mph in 2024)

• More extreme movement profiles, especially on breaking balls

• No need for deep pitch mixes — most relievers throw just two offerings, often with 80–90% usage on one

🔹 Pitch Shape Over Velocity

Velocity opens doors, but shape closes them. Teams have gotten far more precise in identifying which movement profiles produce swings and misses — especially high in the zone or glove-side. For example:

• “Ride” on the fastball (i.e., low vertical approach angle + high induced vertical break) misses bats above the barrel, especially when tunneling with a low-depth slider.

• Sweepers, or big horizontal breaking balls, are now favored for right-on-right or left-on-left matchups. They don’t rely on depth — they rely on missing the bat’s sweet spot altogether.

• Cutters, gyro sliders, and dead-zone avoidance are other shape-centric concepts teams optimize for based on biomechanics and pitch design sessions.

It’s not uncommon for a reliever in High-A to be told to scrap his curveball entirely in favor of learning a sweeper — even if the curve gets strikes — because data shows the sweeper plays better against modern swing planes.

🔹 Deception Is Measurable Now

In the past, “he’s sneaky fast” was a throwaway line. Now it’s a metric.

With motion capture and high-speed video, teams measure:

• Release height and side angle (how unusual is it compared to the league?)

• Extension (closer release = perceived velocity boost)

• Tempo and body timing (do the arm and torso sync or create delay?)

A pitcher throwing 92 with high deception and a +2 extension might outperform another throwing 97 without it. Teams understand this now — and they pay accordingly.

🔹 Specialization is the Point

If a reliever is dominant against lefties and ineffective against righties, that’s not necessarily a flaw. It’s a matchup weapon. In fact, some teams build rosters with as many contrast arms as possible:

• Over-the-top ride guy (high fastball + 12-6 curve)

• Sidewinder with sweep

• Power sinker/slider combo

• Deceptive lefty with mid-80s funk

In other words: don’t build a bullpen full of Swiss Army knives. Build one with scalpels.

This is how elite bullpens are being constructed: not just through raw ability, but through pitch design, intentional usage, and an understanding of hitter psychology. The bullpen is no longer an afterthought. It’s a lab-tested, role-defined machine — and every pitch it throws is measured against expectation.

Case Study: Tanner Scott – From Wild Lefty to Elite Weapon

For years, Tanner Scott was known mostly for two things: throwing hard, and missing the zone. But the Miami Marlins saw more than raw velocity — they saw a pitch profile that could dominate if better managed.

In 2023, Scott posted a 2.31 ERA, 104 strikeouts in 78 innings, and emerged as one of the most effective late-inning lefties in baseball. What changed?

• The Marlins helped him tighten the shape of his slider, giving it a cleaner horizontal break with more consistency.

• They leaned into his strengths: using him heavily against left-handers and in high-leverage matchups, not just the 9th inning.

• His release extension and unique arm slot made his fastball (sitting 96–98) play like 100+, especially up in the zone.

Scott didn’t suddenly gain control — his walk rate was still high. But Miami optimized his usage and accentuated what worked, turning volatility into value. That’s the blueprint.

Team Example: How the Tampa Bay Rays Build a Bullpen Without Big Names

Ask a casual fan to name three Rays relievers from the last five seasons. Most can’t. But from 2019 to 2023, Tampa consistently fielded one of the most effective bullpens in baseball — with minimal payroll investment.

Here’s how they did it:

They Value Pitch Characteristics Over Resume

Rather than targeting “proven closers,” Tampa scouts for:

• Unique arm slots (e.g., sidearm or deceptive low-¾ deliveries)

• Elite pitch shapes with horizontal or vertical extremes

• One-dominant-pitch guys — they’re not scared off by lack of a starter’s repertoire

Example: Andrew Kittredge, a fringe journeyman, became an All-Star after Tampa helped him refine his slider and optimize when/how to use it.

Role Fluidity is the Norm

The Rays don’t assign fixed roles. On any given night:

• The “closer” might pitch the 6th if the heart of the lineup is due

• A soft-tossing lefty might open the game to mess with timing

• A long man might be used as a high-leverage fireman if the numbers dictate it

This fluidity means the Rays can extract high value from unconventional arms, since they never ask pitchers to do what they aren’t built to do.

Development + Deployment = Results

Pitchers like Pete Fairbanks, Jason Adam, and Colin Poche weren’t household names before Tampa. But the Rays optimized their:

• Release mechanics using high-speed motion capture

• Pitch sequencing via game modeling software

• Usage patterns through real-time matchup simulation

They don’t just find guys who can pitch. They create environments where pitchers are most likely to succeed.

In a league where many teams chase velocity or pedigree, the Rays are proof that bullpen value is created, not bought — and that smart design often beats raw stuff.

Building the Bullpen: Front Office Philosophy

Constructing a modern bullpen isn’t just about stashing hard throwers in the back of the roster — it’s a deliberate, layered process shaped by roster constraints, analytical modeling, and development runway.

Where previous front offices might have looked at saves, ERA, or “proven experience,” today’s decision-makers think in terms of pitch profiles, usage projections, and matchup value curves. The question isn’t “Who’s our closer?” It’s “Who fits which window of the game best — and how cheaply can we build it?”

Let’s break down how front offices now approach bullpen construction.

1. Target Identification: Stuff First, Stats Later

In 2024, scouting for bullpen arms starts with pitch tracking data, not stat lines.

The player might be in Triple-A with a 5.00 ERA, but if his fastball has 20+ inches of induced vertical break and a flat approach angle from a high release, he's getting flagged in front office models.

Common targeting filters include:

• Velocity thresholds (e.g., 95+ with movement outliers)

• Spin axis efficiency and seam-shifted wake potential

• Slider vs. fastball tunnel integrity

• Movement profiles that project well against modern swing planes

This is why a player like Yennier Cano, once considered a filler in the Jorge López trade, turned into a dominant reliever in 2023 for Baltimore. The raw movement was always there — it just needed sequencing and confidence.

2. Player Development Alignment

Front offices now see bullpens as extensions of the development system. A reliever isn’t just a finished product — he’s a moldable asset. The key is ensuring:

• Pitch design coaches are aligned with front office models

• There’s room on the MLB staff to give that player the right matchups

• The organization’s game-calling and sequencing strategy enhances his best traits

This is why so many teams convert starters into relievers at the Double-A/Triple-A level. Not because they failed — but because the bullpen allows them to express their best pitches more cleanly.

3. Roster Efficiency & Optionability

Managing a bullpen today is like playing chess with 13 pieces — some of which can be moved freely (optionable) and some that can’t (out of options, Rule 5, etc.).

Smart front offices:

• Keep a shuttle system between Triple-A and the MLB club

• Prioritize relievers with minor league options to create matchup flexibility

• Cycle through fresh arms weekly without losing talent to waivers

The Dodgers and Rays do this exceptionally well. It’s not just about who’s the best 8th-inning guy — it’s about who fits the 40-man puzzle, who can be used and rested efficiently, and who maintains performance under load.

4. Finding Value Where Others Don’t

Relievers are inherently volatile — and front offices have learned to exploit that variance.

They target:

• Post-injury pitchers (where medicals look promising)

• Pitchers with one elite trait but no track record

• Undervalued roles, like multi-inning relievers or matchup-only specialists

They know that a 4.70 ERA in Colorado might translate to a 2.90 in a pitcher's park — especially with a game plan. Value isn’t found on the back of a baseball card anymore. It’s pulled from a 3D spin graph and a TrackMan report.

In short, front offices now treat bullpen construction like a strategic optimization problem: who are the best arms we can deploy under our constraints, against the league’s current hitting profile, in the most impactful moments?

And perhaps more importantly: how can we develop or acquire them before the rest of the league notices?

Hidden Gold: Acquisition Strategies for the Modern Bullpen

If every team has access to pitch data, velocity charts, and biomechanics labs, how do some clubs keep finding diamonds in the rough?

The secret isn’t just in what they’re looking for — it’s where and when they’re looking.

Modern front offices have developed multi-layered acquisition funnels that combine scouting feel, statistical filters, and player dev alignment. Here's how smart teams are identifying bullpen value before it explodes.

1. The DFA Wire and Waiver Market: Low-Risk, High-Stuff Bets

Teams like the Brewers, Orioles, and Giants are constantly scanning the waiver wire for:

• Arms with plus velocity or elite pitch shapes

• Poor results due to bad defense, home park, or misused roles

• Minor tweaks needed (e.g., move to the other side of the rubber, pitch mix rebalance)

🔁 Example: In 2022, the Brewers claimed Bryse Wilson off waivers — a failed starter with pedestrian numbers — but saw potential in his sinker-cutter profile. He became a valuable middle reliever in 2023.

Front offices view waiver claims like lottery tickets. Most fail. A few turn into gold.

2. Minor League Free Agents & Spring NRIs

Once overlooked, minor league free agents are now mined like the Rule 5 draft used to be. The key here is access to:

• Minor league pitch data (which is now widespread)

• Instructional league reports (some orgs scout these like showcases)

• Old track records that can be revived (velocity that dipped and returned, or players who developed new pitches in indy ball or winter ball)

🎯 Strategy Tip: Some clubs maintain a running board of “sleeper arms” they quietly monitor for years — waiting for the moment they show a new pitch or velocity spike.

3. Internal Conversions: Starters-to-Relievers

Organizations now see failed starters as premium raw material. Why?

• They already throw multiple pitches

• They’re used to facing hitters multiple times

• They often gain 1–2 mph in short stints

• They can be molded into multi-inning or matchup-specific weapons

🧩 Example: The Astros’ Bryan Abreu was once a volatile starter with command issues. Shortened up, he became a 100-mph monster with one of the nastiest sliders in baseball.

Some orgs now preemptively tag fringe starters as “reliever tracks” and begin designing their pitch mix for 1–2 inning dominance before they fail as starters.

4. Rule 5 Draft: Scouting for Ceiling, Not Floor

Though the Rule 5 Draft has lost some shine post-COVID, it remains a place to grab:

• High-stuff arms blocked on deep rosters

• Raw but electric prospects stuck in development limbo

• Players from teams without deep analytics infrastructure — untapped value

🛠 Example: The Orioles’ 2022 Rule 5 pick Andrew Politi drew interest for his carry-heavy fastball, despite being buried in the Red Sox system. Teams are no longer scared of incomplete profiles if the raw ingredients are elite.

5. International & Independent League Markets

This is the deepest, least tapped part of the funnel. Some teams scout:

• NPB/KBO arms with MLB-grade offspeed but lower velocity

• Winter league risers who show new life or pitch shape

• Indy ball pitchers with weird angles or untapped velocity

🧪 Strategy Spotlight: The Padres and Giants are known for giving indie-league pitchers a full analytics workup — pitch tracking, biomechanics eval, and developmental roadmap — within weeks of signing.

These acquisition strategies all point to one theme: Relievers are everywhere — if you know what you’re looking for. In a league where 10–15 elite innings can swing a playoff series, the edge often goes to the team that found the next weapon before the rest of the league even knew his name.

Coaching the Modern Reliever

Once a pitcher reaches the bullpen, traditional coaching often treated them as plug-and-play — just stay healthy, throw strikes, and be ready when called.

That model no longer works.

Today’s relievers require hyper-specific development, mental prep for unpredictable usage, and mechanical maintenance under high stress. The coaching process must now mirror how front offices and analysts view relief roles: dynamic, matchup-based, and stuff-first.

Here’s how modern organizations coach relievers for maximum value.

1. Mental Preparation for Chaotic Roles

Bullpen life is volatile. A reliever might go four days without pitching — then be thrust into a 1-run, bases-loaded jam with no outs. That unpredictability is now baked into how teams deploy leverage.

Effective coaching now includes:

• Building daily pregame routines that simulate readiness without over-taxing the arm

• Teaching relievers to mentally “isolate the moment” — focus only on the next pitch, not when it’s coming

• Working with mental performance coaches or sports psychologists to create emotional neutrality and reset triggers

🧠 Coaching Tip: The best relievers can flip a switch instantly. Teams now train that skill explicitly — using surprise bullpen call drills or visualization work in bullpens.

2. Managing Pitch Mix and Usage Fatigue

High-effort pitches are not all created equal. A reliever throwing a high-velocity fastball and low-tilt slider on back-to-back days may appear “available” — but their pitch shapes will likely degrade if mechanics are off by even a fraction.

Modern coaches and analysts now:

• Monitor real-time pitch metrics during bullpens and outings (IVB, spin axis, release height consistency)

• Flag fatigue when pitch movement or release points begin drifting

• Adjust bullpen days around pitch profile decay, not just innings or pitch count

📊 In Practice: If a reliever’s slider shape flattens (e.g., drops from -6" vertical to -3.5"), that can signal latent fatigue — even if the arm “feels fine.” Coaches are trained to spot and adjust for it.

3. Development Never Stops: In-Season Adjustments

In the past, pitch development often ended in the offseason. Now, it happens in real-time during the year.

Relievers are often asked to:

• Add a new pitch mid-season (e.g., switch from slurve to sweeper, or FB/CH to FB/CT)

• Change usage patterns to increase deception or reduce predictability

• Alter mechanics subtly to preserve health (e.g., hip-shoulder separation or spine angle tweaks)

This requires collaboration between:

• Pitching coach

• Analyst/research coordinator

• Biomechanics or S&C staff

• The player himself

🔧 Case Study: The Dodgers helped Evan Phillips unlock a more effective cutter midseason by adjusting his grip and changing how it tunneled off his slider. That in-season tweak made him a late-inning monster.

4. Coaching for Variable Usage

Being a great reliever isn’t just about “stuff” — it’s about consistency across wildly inconsistent usage windows.

Great coaches train relievers to:

• Throw shorter, more frequent bullpens to simulate real usage

• Rebound faster via customized recovery protocols (contrast therapy, movement prep, mobility focus)

• Stay locked in even when their role shifts nightly

Some clubs even use predictive usage modeling to simulate scenarios for their bullpen arms — helping them anticipate likely game situations 24–48 hours in advance.

🔁 Best Practices: Elite bullpens often use bullpen days to simulate a game appearance — 15–18 pitch ups with full velocity, sequencing, and rest-to-effort pacing.

5. Coach-Player Communication is Everything

In a bullpen built on trust, the line between coach and analyst is blurring. Coaches must be fluent in:

• Rapsodo/TrackMan output

• Biomechanical language

• Physical recovery metrics

• In-game matchup probabilities

But they must also build genuine relationships — because no amount of data can replace a reliever telling you, “I don’t feel right.”

The best modern bullpen coaches know when to push and when to protect. When to tweak, and when to trust. Their job is to translate the data into feel — and vice versa.

Matchups & Leverage: The Usage Revolution

The old bullpen script — setup man in the 8th, closer in the 9th — has been shredded. Today, teams structure bullpen usage around leverage, not innings, and matchups, not tradition.

In this modern system, relievers aren’t just throwing earlier or later. They’re being surgically deployed based on real-time win probability, platoon splits, swing paths, and lineup context.

The closer still exists — but in name only.

1. The Rise of Leverage Index (LI)

Leverage Index quantifies the pressure of a given moment. A 9th-inning, one-run game with runners on is high-LI. A 7th-inning, 5-run lead is low-LI.

Smart teams now deploy their best reliever based on leverage, not inning. In other words:

• Your best arm might pitch the 6th if the opposing 2-3-4 hitters are due with the bases loaded

• The 9th could go to your 3rd- or 4th-best arm if it’s a low-LI moment

🧠 Strategy Note: The Guardians, Dodgers, and Blue Jays are among teams that explicitly use leverage models to guide bullpen sequencing.

2. Real-Time Matchup Modeling

Before every series, modern bullpens receive:

• Platoon profiles for every opposing hitter

• “Danger zones” showing where their pitches are most/least effective against that lineup

• Heatmaps predicting where their pitch shapes will play best

In-game, this information informs not just pitch selection — but pitcher selection. Coaches and analysts collaborate to decide:

• Who faces the top of the order?

• Who handles pocketed platoons?

• Who handles lefty-lefty threats with sweepers or sinkers?

📊 Example: A righty reliever with a horizontal cutter and reverse splits might be chosen over a lefty to face a lefty like Kyle Schwarber — because his swing path favors sweeping action over traditional LHP angles.

3. Role Fluidity & Opener Systems

Some relievers are now:

• Openers — starting games to disrupt platoon advantages

• Bulk inning bridges — going 2–3 innings after a short starter

• Multi-inning firemen — entering with runners on and staying for multiple frames

These roles require relievers to be mentally and physically prepared for unpredictability. Coaches condition for that, and front offices build rosters to support it.

🧩 Case Study: The Rays have mastered this — routinely cycling through bulk relievers like Josh Fleming or Yonny Chirinos in tandem roles, saving high-leverage arms for later.

4. Hot Hand vs. Matchup: The Balancing Act

Despite all the data, emotion still matters. Some relievers get hot — their feel is sharp, their confidence high. Managers must decide:

• Do we ride the hot hand or stick to our script?

• Does the data say this matchup plays, even if the pitcher is “off”?

The best bullpens blend real-time observation with pregame planning — and have trusted communication loops between coaches, relievers, and analysts to adapt on the fly.

5. Closers Are Now "Game-End Specialists"

The closer still exists, but not every team uses one the same way. A few models include:

• Matchup Closer: Best reliever pitches vs. toughest part of the order, whenever that happens

• Floating Closer: Used in the 8th/9th depending on leverage, but not locked into a single inning

• Traditional Closer: Still gets the 9th regularly (e.g., Josh Hader, Emmanuel Clase)

🔍 Reality: Even teams with named closers rarely use them in rigid, every-save-situation roles anymore — because not all saves are equally difficult.

Bullpen usage today is dynamic, data-informed, and matchup-specific. The reliever's job is no longer just to throw strikes — it’s to fit a precise moment. And the manager’s job is no longer just to follow a script — it’s to maximize each out like it's a finite resource.

What This Means for Player Development

As the bullpen evolves at the Major League level, the downstream impact on amateur and minor league player development is massive — and still unfolding.

Relief pitching is no longer a fallback or a consolation role. For many pitchers, it’s now a primary development track, with its own identity, training needs, and value ceiling.

If you’re developing pitchers in 2025, you’re no longer just building starters — you’re building matchup weapons, leverage arms, and stuff-first specialists.

1. Relievers Aren’t “Failed Starters” Anymore

The old progression — start until you can’t, then move to the bullpen — is outdated. Forward-thinking orgs now:

• Identify bullpen candidates early (based on arm action, velocity potential, pitch mix fit)

• Design specific training for short-burst power and high-rep quality

• Build psychological profiles for relievers — fast reset ability, comfort with chaos, readiness on call

🧠 Shift in Mindset: Being a reliever is now a legitimate career path — one that can fast-track a player’s ascent if his traits align.

2. Development Should Match the Role

Relievers don’t need six-pitch mixes. They don’t need 90-pitch build-ups. They need:

• Two elite pitches that tunnel well

• Consistent release and tempo

• A routine that holds up under irregular usage

Player development programs should adjust:

• Throwing programs to emphasize late-game readiness (e.g., mid-week intensity peaks instead of weekend peaks)

• Bullpen sequencing practice (working in high-stress reps instead of long bullpen pens)

• Recovery protocols tailored to variable workloads (some days up-and-down with no game action, others on 1-day rest)

🔁 Practical Tip: Develop mini-bullpens — 15–20 pitch “up-downs” that simulate live action under fatigue and game pace. These prepare relievers better than 40-pitch flatground sessions.

3. Train the Traits That Get Called Up

What gets a reliever promoted isn’t his ERA. It’s:

• A pitch that misses bats in the zone

• Command within a tight, repeatable release window

• A secondary pitch that plays against same-side hitters

• The ability to dominate for one inning, right now

Teach to those traits. If a reliever can throw 96 with a plus sweeper, build the plan around that — not polishing up his changeup for balance he’ll never need.

4. Build Relievers With Data in Mind

Minor leaguers and college players need to learn how their pitch metrics translate to higher levels. This includes:

• Understanding vertical approach angle and induced vertical break

• Knowing which pitch pairs tunnel well and why

• Learning which hitters chase which shapes — and how to use it

Coaches can help players:

• Use feedback tools like Edgertronic, Rapsodo, and TrackMan to refine pitches

• Study whiff zones vs. contact zones

• Experiment with grips during side sessions based on movement targets, not just feel

🎯 Dev Hack: Even at the amateur level, low-budget tools like PitchAI or Pocket Radar + video can begin simulating pro-level feedback.

5. Teach the Reliever Mindset Early

Relievers operate in chaos. They warm up fast. They enter mid-inning. They inherit jams. And they might not throw for three days — then pitch three days in a row.

The earlier young pitchers can be exposed to that mental model, the better they’ll adapt when the call comes.

🧠 Mindset Drill: Have players “surprise start” a live inning with a 90-second notice. No time to warm up mentally — just go. It simulates the real-world demand of a phone call mid-7th.

Modern player development doesn’t just build velocity and strikes. It builds relievers with role awareness, matchup clarity, and high-leverage readiness — because that’s what today’s game demands.

The Future of the Bullpen

The bullpen isn’t just changing — it’s actively reshaping the way baseball is played, coached, and built. And the evolution isn’t slowing down.

What began as a shift in how teams use relievers has now transformed into a complete rethink of who becomes a reliever, how they’re developed, and what value they bring.

But even now, we’re only seeing the early stages of what’s possible.

Where It’s Headed

Looking forward, several emerging trends could push the modern bullpen even further:

• AI-Driven Matchup Decision Engines: Teams are already experimenting with in-game systems that suggest reliever matchups based on live data — not just pregame charts.

• Biomechanical Customization: Motion capture is evolving from “diagnostics” to “design.” Soon, relievers might alter mechanics mid-season based on stress markers or shape decay — automatically flagged by biomech software.

• Pitch Design Arms Race: Every offseason, more relievers enter with optimized pitch shapes built in labs. The best organizations will be those who can evolve faster than hitters adjust.

• Hybrid Roles Becoming Standard: The “bulk reliever,” the “3-out fireman,” and the “roving leverage arm” will soon be standard parts of every bullpen. Players will train into these identities, not stumble into them by accident.

Risks and Tensions

With increased leverage and usage, however, comes increased strain:

• Health management will become more complex as workloads fluctuate nightly

• Player psychology will be a bigger differentiator — as volatility and unpredictability define bullpen careers

• Labor market tensions may grow, as relievers with elite results but no “closer” title remain underpaid by traditional metrics

Front offices and coaching staffs must collaborate more closely than ever to balance short-term deployment with long-term sustainability.

Bottom Line

The bullpen is no longer a side room. It’s the main stage. And the teams who treat it with the same nuance and precision as their starting rotations and batting orders are the ones who’ll stay ahead.

If you’re building a pitching staff in 2025 and beyond, you don’t just need five good starters. You need seven nasty relievers. Each with a role. Each with a plan. Each with a pitch you don’t want to see in a tie game.