Robert Preece was with Denver at the time of the stabbing. Preece claims a large group of men came up behind them when they were leaving a local bar after the game.
Preece has identified one of those men to be 21-year-old Michael Montgomery, who was arrested for stabbing Denver, then later released.
Preece told sister station KGO-TV in San Francisco that he swung a beach chair at Montgomery after the 21-year-old approached them with a knife.
"Why would you carry a knife if you weren't anticipating something was going to happen, or if you weren't going to do anything, why were you looking for trouble?" Preece said.
Preece said he swung the chair because he was trying to protect his brother.
Montgomery's father claims his son stabbed Denver in self-defense.
Even though he's been released, San Francisco police continue to investigate Montogomery's claims, but won't file charges until there's evidence that could lead to a conviction.
KGO-TV and the Associated Press contributed to this report.