Since patch 4.20 - 4.21 I have had fps drops.
So after I updated league to 4.20, I noticed that once in game my frames were alot higher than normal. However once in lane they started dropping from 100 all the way to 10. Whenever we trade or someone ganks our lane my frames would change from 10 to 0-3 frames. Team fights....... there are no words, its pretty obvious what happens, 0 frames. I did a little research onto why this was happening and it turns out I'm not the only one with this issue. Other players have also had problems with their fps since the most recent patches. What's also odd is I can play on High graphics for the first 5 minutes of a game no problem, and maybe close to around mid game the frames drop and turning the graphics down does not change anything. This also happens on every gamemode. Leaving apps up in the back while I play/leaving them off does not affect LoL. I really hope that this has something to do with LoL and not my computer, since i've never had a problem until patches 4.20-4.21.
Also, please just try to fix the game and stop adding new gamemodes, skins, and champions for a broken game. Fix the game and we'll be happy. (most of us)