Freezing during team fights

Honestly I've only seen this before during severe ping lag. My last match I my computer had 250-375 fps and 21 ping. So it wasn't "normal" lag. Anything I was doing anything other than hitting a minion I could hear spells and sound effects I could press buttons but there would be a 2-5 second video freeze, and people would slide across the screen and I normally ended up dead. The only programs I had running was the league client and Skype (which I always use when playing). Does anyone know what might cause this?