Under current rules, a starting pitcher must pitch five innings to get a win, whereas a reliever need only pitch a third of an inning to get a win. When the go-ahead run (that is, the run that puts a team ahead and the other team does not tie or get the lead for the remainder of the game) is scored, the winning pitcher is the last pitcher of the half-inning before the go-ahead run is scored, unless that pitcher is a starter with less than five innings pitched, in which case the official scorer awards the win to one of the relievers. This gives discretion to the official scorer. I would propose the following change which would give a starter more of a chance for a win is to give the first pitcher with the most outs in the entire game the win if the go-ahead run is scored before a reliever takes the mound. This would end situations where a starter pitched 4-1/3 innings and a reliever pitching only one or two innings gets the win at the scorer's discretion when the go-ahead run was scored during the starter's tenure. This rule would cover five inning games as well as exhibition games where pitchers are limited to a certain number of innings.
He must pitch a minimum of 5 complete innings.
There is no limit in regards to how many innings a Starting Pitcher must pitch in the Major League Baseball All Star game, a team can be winning and the Starting Pitcher could pitch only 2 innings but because All Star games have different rules, they can be given the Win.
Four consecutive innings if she is the starting pitcher. There's no minimum number required for relief pitchers.
A starting pitcher needs to pitch at least 5 innings to get the win. Any subsequent pitcher can get the win even if he only retires one batter (or base runner). If the starting pitcher leaves with the lead but without pitching 5 innings, and his team maintains that lead, the official scorer can decide which pitcher to give the win to.
In a Major League Baseball game, Starting Pitchers can pitch as many innings as needed, it is up to the discretion of his Manager however Starting Pitchers must pitch 5 innings in order to qualify for a win.