Mac - El Capitan Game Crashes After Champ Select and Lock-In in Custom Games

I was going to try out my Gnar in a custom game just to see how it plays and as I lock it in during champ select and the counter goes to zero and the screen loads, nothing loads, my mouse cursor remains normal and nothing happens. Im on a MAC El Capitan, so I do Command Option Escape and it says my game has crashed. This has happened several times. Anyone else have the same problem? A few of those time, I can hear the game beginning as my champ enters Summoner's Rift but the screen was blacked out. Edit: Not just custom games, but also bot games, and presumably even normals.