CRASH

When ever I launch league I can go perfectly through champ select and navigate the launcher just fine, however whenever I attempt to play a game the second I get into the loading screen no champions load and my game crashes, I then repeatedly press "Reconnect" but even then when it opens up a League tab no champs load and the game continues to crash. iMac (Retina 5k, 27-inch) OSX- El Capitan V.10.11 Processor 3.5 GHz Intel core i5 Memory 8 GB 1600 MHz DDR3 Graphics AMD Radeon R9 M290x 2048 MB