It happened at some point during the United States' 2-0 win in the CONCACAF Nations League final at AT&T Stadium in Arlington, Texas ... when Team Mexico fans clearly had enough of a gloating U.S. supporter.

Check out the footage ... as the man decked out in red, white and blue cheered on his squad -- a Team Mexico fan tried to sock him in the face.

All hell then broke loose ... as multiple people jumped into the fracas to attempt to land some punches.

The fight lasted roughly 30 seconds .. with at least four people throwing hands. Throughout the fracas, others in the stadium chucked their drinks at the combatants.

Mercifully, the tilt ended when the U.S. supporter was pushed over a row of chairs.

It's unclear if anyone was arrested -- but it was hardly the first time during the evening that fans misbehaved ... as the match had to be stopped multiple times due to fans chanting homophobic language.

CONCACAF released a statement late Sunday night condemning the actions ... saying, "It is extremely disappointing that this matter continues to be an issue at some matches."

"We will continue to urge fans to support their teams positively and with respect for the opposition and all participants in the game."