One of the best young hitters in the MLB looked more like a Little Leaguer on Tuesday ... 'cause Ke'Bryan Hayes forgot to touch 1st base on a home run -- and the gaffe REALLY cost his team.
The Bad News Bears moment all went down in the bottom of the 1st inning of the Pirates' game against the Dodgers ... when Hayes cracked a shot to the opposite field.
The ball was a bullet that hit the foul pole, giving Hayes a home run ... but there was just one problem -- he never tapped 1st on his way around the diamond!