MLB's Tommy Pham Makes Obscene Gesture During Spat With Fan

Tommy Pham grew so frustrated with a fan during the Pirates' tilt vs. the Angels Wednesday, he busted out an obscene gesture toward the person ... and it's all probably going to result in a stiff fine.

The Pittsburgh left fielder's spat with a Halos supporter began during the fifth inning of the Buccos' matchup with L.A. at Angel Stadium ... when a man clad in red leaned over some railing and touched Pham while he was digging for a ball in the dirt.

The Pittsburgh star clearly didn't appreciate the physical interaction ... and after throwing the baseball to the infield, he and the guy seemed to quarrel for a few more minutes.

At one point, Pham seemed to grow so frustrated with the words the dude was spewing -- he put his hand near his privates and made an X-rated motion.

The scene was actually captured on the game's broadcast -- and when Pham was making his move ... one of the guys on the call stated, "Oh, there's Tommy Pham, as he says, 'Hello,' to the crowd."

Pham and the man seemed to feud a bit more ... before the inning mercifully ended.

So far, no punishment yet from MLB -- but we're sure the league will make his wallet a bit lighter at some point later this week.