Innings Pitched measures the total number of innings a pitcher pitched over the course of a season as measured by the total number of hitters and baserunners put out while the pitcher was in the game.
More about Innings Pitched Leaders
While the number of complete games pitched has dropped dramatically in a generation, the number of innings pitched by league leaders has also decline, though not nearly as much. Currently, pitchers who throw 225 innings or more will be among the league leaders; twenty or so years ago approximately 250 innings were required to be among the league leaders. Knuckleball pitchers, though rare, will sometimes be among the league leaders in innings pitched because throwing the knuckleball isn’t as strenuous as throwing the more “traditional” pitches most pitchers throw.