What is an RP in Baseball?

In baseball, an RP (Relief Pitcher) is a player who typically enters the game during the middle or late innings to replace the starting pitcher and help the team maintain or decrease the opponent’s lead. The RP is primarily used to protect the team’s lead and keep the team in contention for a win. In the modern game, RPs are often counted on to provide more than just a few innings of relief pitching.

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History of the Relief Pitcher

The role of the relief pitcher has evolved over the years. In the early days of baseball, the pitcher was responsible for the entirety of the game and would often throw over 200 pitches per game. As the game evolved, the rules changed, and the pitcher was limited to nine innings of work. This created the need for someone to come in and give the team a break in the later innings.

The first RP to make an appearance in the modern game was George Zettlein in 1876. Zettlein was a left-handed pitcher who was used to relieve the starter and help the team maintain a lead. He would often throw between two and five innings, providing the team with a much needed break from the starter.

The Rise of the RP

The role of the RP continued to evolve over the years, and eventually the usage of the RP became more commonplace. In the 1950s, teams began to employ multiple RPs, with one reliever typically entering the game in the sixth or seventh inning and another in the eighth or ninth. This allowed the team to have a more reliable bullpen and better protect their lead.

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During this time, some teams began to employ the “closer”, a RP who was used to protect the lead in the ninth inning. The closer would come in with a specific job; protect the team’s lead and close out the game. This role was often filled by a hard throwing pitcher who could get out of tight situations and keep the opponent off the scoreboard.

Modern Use of the RP

Today, the RP is an integral part of the game. Teams employ multiple RPs to provide them with a variety of arms to choose from and protect their lead. Many teams employ a “closer” as well as multiple “setup” men who can come in and shut down the opponent’s offense in the later innings.

The RP is also used to give the team’s starters a break. Many teams will use the RP to replace a starter who has gone deep into a game and needs a break. This allows the team to keep their starters fresh and also gives them a chance to rest and prepare for their next start.


The RP has been a part of the game of baseball for over 140 years and is a valuable part of any team’s roster. The RP is used to protect leads and give the team’s starters a break. They are often counted on to provide more than just a few innings of relief, and can often be the difference between a win and a loss.