teamfight lag

So i'm hooked up via Ethernet, I have very good internet. i get an average of 27 ping when in game but for past few days of playing the game it seems like things gotten weird. when i get in game my ping is normal. then later in the game when there are teamfights up to 2v2+ my ping shoots up to 280 freezes my game and skips ahead a few secs and then it cuts to me getting killed (most of the time). this happens almost every time and the only time whenever engage or an random spike every so often. and pls don't say i need better internet because i test my ping before i get in game and its 11ms and i can play other games just fine with 0 lag. whatever this is it's on leagues side.