<P> The decisions are awarded by the official scorer of the game in accordance with the league's rules . The official scorer does not assign a winning or losing pitcher in some games which are forfeited, such as those that are tied at the time of forfeiture . If the game is tied (a rare event), no pitcher is awarded any decision . A pitcher's winning percentage is calculated by dividing the number of wins by the number of decisions (wins plus losses), and it is commonly expressed with three decimal places . </P> <P> In Major League Baseball, the winning pitcher is defined as the pitcher who last pitched prior to the half - inning when the winning team took the lead for the last time . </P> <P> There are two exceptions to this rule . The first is that a starting pitcher must complete five innings to earn a win (four innings for a game that lasts five innings on defense). If he fails to do so, he is ineligible to be the winning pitcher even if he last pitched prior to the half - inning when his team took the lead for the last time, and the official scorer awards the win to the relief pitcher who, in the official scorer's judgment, was the most effective . </P> <P> The second exception applies if the relief pitcher who last pitched prior to the half - inning when the winning team took the lead for the last time was "ineffective in a brief appearance" in the official scorer's judgment, in which case the win is awarded to the succeeding relief pitcher who, in the official scorer's judgment, was the most effective . </P>

Who gets the win if a pitcher doesn't go 5 innings