Willson Contreras completely lost it after a strikeout Monday night ... throwing a temper tantrum that resulted in one of his coaches being hit by a bat.
The wild scene unfolded in the seventh inning of the St. Louis Cardinals' matchup with the Pittsburgh Pirates at Busch Stadium ... just after Contreras got rung up on a pitch that was low in the zone.
The Cards' catcher, at first, looked like he was going to walk away from the matter with just a few words -- but once he got near his dugout, he exploded.