A Boston Red Sox prospect uncorked a haymaker on a pitcher after he was beaned during a game Thursday night ... and the punch was so violent, it ignited an all-out brawl on the field.
The wild scene went down during the Portland Sea Dogs' minor league baseball game against the Binghamton Rumble Ponies ... when Sea Dogs first baseman and Sox prospect Tyreque Reed was drilled on the arm during the third inning.
You can see in footage of the play, following the hit-by-pitch, pitcher Marcel Renteria -- a New York Mets prospect -- appeared to say something to Reed that set him off.