L.A. Rams players weren't the only ones taking a beating from Dallas on Sunday ... their fans were, too -- with one dude getting KO'd by a Cowboys fan during a parking lot brawl.
The SoFi Stadium parking lot brawl was caught on video as the Rams were losing to "America's team."
The video shows several people in Rams and Cowboys jerseys going at it as a few people attempted to keep the peace.
But, nobody listened ... and then, out of nowhere, a guy in a #88 jersey (CeeDee Lamb, Dez Bryant, Michael Irvin, Drew Pearson?