A panel of judges at Portsmouth, Hampshire, reached the verdict on Ian Russell after 30 minutes. He will be sentenced today.
Leading Physical Training Instructor Russell, 36, based at HMS Rayleigh in Plymouth, was accused of shattering Gary Curtis's nose in six places, injuries that required two operations. Mr Curtis, 31, said that during the match between his club team, Havant, and the Royal Navy side last October, Russell pinned him to the floor with his knee and punched him square on the nose, having already kicked him in the head. Russell denied causing grievous bodily harm.
Mr Curtis, who has not played since the incident, said: 'There are what I call rules of the jungle, but that was so far beyond the rules of the jungle even. It was a horrible punch.'