MANKATO, Minn. (AP) - Authorities in Mankato have released surveillance video of a fight that led to assault charges against former Minnesota Gophers quarterback Philip Nelson.

Nelson is accused of attacking former Minnesota State, Mankato football player Isaac Kolstad in a Mankato entertainment district after an argument May 11.

Reports say the video shows Nelson talking with a friend of Kolstad's when Kolstad comes up from behind and throws a punch that sends both Nelson and the friend to the ground. Kolstad is walking away when he is struck by another man from behind and hits the ground.

The video then appears to show Nelson kicking at Kolstad.

Nelson's attorney, Jim Fleming, has argued that Kolstad's serious head injury was caused not by Nelson but by the man who first struck Kolstad.