We now know why Logan Webb pitched poorly in the MLB All-Star Game earlier this summer ... he just admitted he was wildly hungover as he was toeing the rubber at the Mid-Summer Classic.
The San Francisco Giants star made the revelation on Wednesday's episode of "The Chris Rose Rotation" ... explaining that he went just a little too hard in Arlington the night before the big July game.
He said following the Home Run Derby festivities on Monday evening -- the MLB threw a party for the players and their families at the Dallas Cowboys' The Star facility .