To put starting pitchers in perspective it is sometimes nice to see how they rank amongst each other. I put a page up with a ranking of all MLB starting pitchers in 2013. That table was too big for a single post. The below table shows a list of top 30 MLB relief pitchers for the 2013 season.
Koji Uehara tops the list with a 5.0 WAA, about half that of top MLB player, Clayton Kershaw. WAA represents the number of wins a player brought to his team. Relief pitchers don’t pitch a lot of innings. Uehara’s 74 innings pitched is about 1/3 that of a full time uninjured starting pitcher. He can’t possibly rack up the WAAs because of his lack of playing time. Relief pitchers are part of a squad that must pick up the end of most all games in some type of fashion. It is the performance of the entire relief squad as a team that either helps or hurts a team. Having a relief pitcher contribute a +5 WAA is a huge contribution to a relief squad as well as a team.
Relief pitching is a type of pitcher. I chose to define a relief pitcher to qualify for this list as someone who pitched > 35 innings, had a G/IP < 2, and pitched more relief than starts. This model does not recognize the save stat. The save stat is simply an award given out that has no meaning in the mathematics of baseball. Many of the pitchers below have been given quite a few saves. Mathematically, runs given up in the 6th, 7th, or 8th innings count as much as runs given up in the 9th. In the end the team who gives up the fewest runs wins the ballgame.