Analyst James LaFond studied 1,675 acts of violence that took place between June 1996 and May 2000. At the request of the FBI Academy in Quantico, Virginia, he then analyzed the incidents in his study that led to a knockout.
What gets me the most is how easy one can get knocked out. Sucker-punches are pretty typical, and tend to lead to bad things for the recipient.
Empty hands can be ugly things. Weapons (don’t limit yourself to guns and knives) can be uglier. Do your best to avoid the fight in the first place.