You most certainly can blindside someone in a brawl.
Let's just set up a scenario: Read2go, LL, and a bunch of other posters get in a brawl with Kcourt, and a bunch of his friends. Kcourt see's LL is fighting one of his friends with his back turned to him, Kcourt goes up and punches LL in the back of the head, LL is knocked out and has to go to the hospital.
What kcourt did to LL would be considered a blindside shot, and a cheap shot.
Not saying this is what happened in the Frease Gates incident, just trying to make the argument that many UC fans have argued against, and that is, there can be cheap shots in brawls.