[Crash] Mac client - game always instantly crashes

I have a MacBook Pro (Retina, 15-inch, Mid 2014) running OS X Yosemite 10.10. I installed the lol client, it downloaded the 4.21 patch. Everything seemed to be stable I played lol a few matches and then the game crashed. I pressed reconnect and it instantly crashed again ( as soon as the game loads up it just turns of, i'm taken back to my lol client with a message the game has crashed and i can only press 'reconnect' and if I do it will crash again ). And it's the same for all games from then.

I can fix it by reinstalling LoL, i can play one or two matches with a clean install until the first crash after which I have to reinstall LoL again.

Maybe someone experienced this and has a better way to fix the issue than reinstalling LoL?

Thanks