Angels star Anthony Rendon -- a former World Series champion -- was involved in a heated confrontation with an A's supporter following L.A.'s loss on Thursday ... one where he grabbed the fan and then attempted to take a swipe at the guy's face.
TMZ Sports has learned ... the altercation happened just seconds after the Halos lost at RingCentral Coliseum in Oakland, 2-1 -- when Rendon believed a fan had call him "a bitch" near their dugout.
The L.A. third baseman was he was so upset over it, he locked his hand around the guy's tee, and pulled him down to the railing.