In baseball, a loss (denoted by L) is charged to a pitcher when that pitcher, in a game lost by his team, is charged with allowing the run that gives the opposing team a lead they do not relinquish for the remainder of the game.

The pitcher who gives up a hit to score the "go-ahead run" does not necessarily receive the loss. For example, in a tie ball game, if pitcher A walks a batter and then is relieved by pitcher B who then give up a home run, the first run allowed is recorded to pitcher A and the second to pitcher B. Thus, pitcher A gave up the run that gave the opposing team the lead, and pitcher A will be credited with the loss if the other team does not relinquish the lead, even though pitcher B was on the mound when the go-ahead hit occurred.