Mac in game screen stuck

My friend who has a mac computer is trying to play LOL and when the game opens the screen turns white. He tried to Command+Tab back to it, the screen changed and its stuck. So in other words for some reason, LOL only refreshes screens when you Command+Tab out of it and back into it. so we tried it multiple times and when we did it it shows the screen but is stuck on one frame. On my side of the line i can see everything he does like flash or moving or something, but he cant see what is going on. Please someone i would like some help on this! (Although you have probably never heard of this issue...)