Mac black screen solve :)

1.Open the League folder under Applications 2.Open Package Contents 3.Contents 4. LoL 5.Config 6.Open the file Game.cfg with textEdit 7.Go under General and change WindowMode from 0 to 1

This will change you from Fullscreen to Windowed mode 0=Fullscreen 1=Windowed 2=(I think) Borderless

I HOPE THIS WORKS FOR YOU GUYS TOO!