It was a rough day to be a White Sox supporter on Sunday … ’cause as the MLB team got smacked by the Diamondbacks — one of their fans got leveled during a fight in a festival pit too.

The crazy scrap happened at SeatGeek Stadium in Illinois during Summer Smash — a three-day show headlined by Travis Scott, Playboi Carti and Chief Keef.

In video from the scene, you can see a young Sox fan in a grey Chicago jersey got into a tiff with a man in a pink shirt who had been situated on another side of a barricade.

Unclear why the guys had beef — but just seconds into the altercation, the CWS fan was decked to the ground by a straight right hand.

As he stumbled to his feet, the White Sox supporter for some reason tried to get back into the fight — only to be leveled once more by a series of slaps and yet another big punch.

The guy eventually got up again, and after exchanging some words — he finally left … which delighted the crowd.

The White Sox, meanwhile, didn’t fare much better in their fight with Arizona on Sunday — losing to the Snakes, 12-5.

As for the Chicago Sky, they lost on Sunday too … although star player Angel Reese at least appeared to enjoy her night at Summer Smash.