Several fans got into a crazy brawl in the stands at the Chiefs vs. Broncos game on Sunday ..

. and things turned so violent, TMZ Sports has learned one of the guys involved was actually charged with assault. The incident took place at some point during Kansas City's 16-14 win over Denver at Arrowhead Stadium.

pic.twitter.com/O2zbXUyM6B According to video shot by a bystander, it all appeared to begin when a Patrick Surtain II supporter started throwing hands at a neighboring fan.

You can see in the clip that security attempted to break things up ...

but it only resulted in the Surtain fan tumbling down several rows of seats. Once the Surtain backer returned to his feet, he began telling security, "I didn't swing on nobody" ..

. but then, suddenly, another Broncos fan raced in and threw two jabs at a guard's face. The crowd around the fighters stepped in to mercifully put an end to the scuffle.

According to court documents we obtained, one of the combatants, Colorado native Joseph Mascarenas , was charged with assault. The docs show his arraignment has been slated for December 27..