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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.

Contreras went back toward the homeplate ump, got in the guy's face, and screamed. Things got so intense, his manager had to physically pull him away from the area -- but Contreras' outburst continued.

At one point, following his ejection, Contreras hurled his bat in d

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