[Crash] Dying freezes/crashes my game. Mac!

(There used to be a lot of bugsplat and crashes but Riot seemed to fixed that couple of weeks ago. Thank you Riot! :D )

I play on a 4 year old mac. My loading speed is slow as a snail but I'm not worried about that, since the gameplay is smooth.

OS X Version 10.9.5 Processor 2.4 GHz Intel Core i5 Memory 4 GB 1067 Mhz DDR 3

The only problem that I've been encountering with playing league on my Mac however, is the temporary freeze that I die, before the screen turns grey, my entire screen sort of lags for a brief moment. I am used to this happening to me, so even whenever I cannot see the source of damage but my screen freezes a bit, I know that I just died from some kind of unseen threat.

But the real problem is the crash. I was playing on TT Hexakill, and I was 1-1 with Lux. I was jumped by 5 people on their team and immediately got shredded, however, before my HP bar on my screen even reached 0, my screen just froze with me at about 200~ HP and their entire team surrounding me. The sounds from the map Twisted Treeline were playing, but nothing else. I couldn't move my mouse, or lower my brightness or volume.

This death made my game crash in a weird manner that I've never seen before. Usually when this happened, I was able to Force Quit league and restart the client to join the game again. Not this time apparently, I had to force shut down my mac, and I couldn't turn it back on for another 5 minutes.

I'm not sure why death causes little bit of freezes / sometimes even crashes. Maybe because my screen turns grey? I can't see what would go wrong with the codes to crash a player from the game, by removing the ability to move or cast spells? I'm pretty sure it's Mac related.