What is a Relief Pitcher in Baseball
A relief pitcher is any pitcher who enters the game after the starting pitcher — responsible for protecting a lead, keeping the game close, or shutting down the opposing offense in late-inning situations.
A relief pitcher (also called a reliever or bullpen pitcher) is any pitcher who enters the game after the starting pitcher has exited. While the starting pitcher's job is to pitch as deep into the game as possible — ideally 6–7+ innings — relievers are specialists brought in for specific situations: protecting a lead late in the game, getting out of a jam, or facing a single batter in a matchup-based move.
The collection of all relief pitchers on a team's roster is called the bullpen.
Types of Relief Pitchers
Closer
The closer is the team's most trusted reliever, generally brought in to pitch the 9th inning when the team holds a lead. Closers are specialists in high-leverage, high-pressure situations. A successfully completed save in the ninth inning is logged as a save — the primary statistical gauge of a closer's performance.
Notable closers: Mariano Rivera (Yankees), Trevor Hoffman, Craig Kimbrel, Edwin Díaz.
Setup Man / Setup Pitcher
The setup man typically pitches the 7th or 8th inning to hand a lead to the closer. Setup men are often the second-best reliever on the staff and must themselves be effective in high-pressure situations. Their performance is captured by holds (stat given when a setup man enters with a lead, records at least one out, and leaves without surrendering the lead).
Middle Relievers
Pitchers who handle innings 4 through 6 — often picking up the game when the starter tires, struggles, or is on a pitch count. Middle relief is a deep category that includes long relievers (capable of pitching 2–4 innings) and situational specialists.
Left-Handed Specialist (LOOGY)
A pitcher used specifically to face one or two left-handed batters in critical situations. Their value lies in the platoon advantage — left-handed pitchers have statistical advantages against left-handed hitters. The three-batter minimum rule (instituted in 2020) limited the pure LOOGY role, requiring pitchers to face at least three batters (or end the inning) before being replaced.
Opener
A modern strategy where a reliever "opens" the game — pitching 1–2 innings — before a bulk pitcher takes over. Used by analytically aggressive teams to exploit matchup advantages or protect a starting pitcher's workload.
Key Statistics for Relief Pitchers
| Stat | Definition |
|---|---|
| ERA | Earned Run Average — runs allowed per 9 innings |
| WHIP | Walks + Hits per Inning Pitched — measures baserunners allowed |
| K/9 | Strikeouts per 9 innings |
| BB/9 | Walks per 9 innings |
| Saves | Recorded when a pitcher enters with a lead of ≤3 runs with tying run on deck and finishes the game |
| Holds | For setup men; entering with a lead and maintaining it |
| Blown saves | Entering in a save situation and surrendering the lead |
| FIP | Fielding Independent Pitching — ERA-like metric based only on strikeouts, walks, HBP, and home runs |
Relief Pitcher Workload
Relief pitchers typically throw 1–2 innings per appearance and may pitch on consecutive days when needed. Teams have expanded bullpens to 13–14 pitchers on their active roster to manage workloads and create matchup options. Overusing relievers on back-to-back days — especially in high-leverage situations — is a significant managerial challenge. Each reliever's workload is tracked by pitch count, and most managers avoid extending a reliever much beyond 20–25 pitches in a single outing.
The Evolution of the Bullpen
Historically, starting pitchers were expected to complete games. The complete game was routine in the early 20th century. As the game evolved:
- 1970s-80s: The closer role took hold — one dominant reliever for the final inning
- 1990s: Closers became stars; Mariano Rivera elevated the role to elite status
- 2010s: The opener strategy (Tampa Bay Rays) challenged conventional pitching usage
- Modern era: Analytics drive extreme bullpen specialization; starters who go 5+ innings are increasingly rare; teams carry 8–10 relievers
Famous Relief Pitchers
- Mariano Rivera (Yankees) — Considered the greatest reliever ever; 652 saves; one pitch (cutter) dominated for nearly two decades
- Trevor Hoffman (Padres/Brewers) — 601 saves; "Hells Bells" entrance created relief pitcher mystique
- Billy Wagner — 422 saves; among the hardest-throwing left-handed closers in history
- Craig Kimbrel — Dominant peak; unusual delivery; over 400 career saves
- Rollie Fingers — 341 saves; Hall of Famer who helped define the modern closer role