Why is it that the game always jerky:?

I'm the only game playing League of Legends and for a few days it has struck me that I have laggs (i.e. FPS drops) from time to time. The whole thing sometimes drives me to the extreme like centrifugal forces when I suddenly have to fight 5 men with 10 FPS in a team fight. I know that my PC is not the best or the newest, but I look at the CPU usage etc. In the background all the time. And that goes up to a maximum of 50% usage, that's not that much is it? At that time I could still play normally without any stutters, but recently they have just started appearing every now and then… And especially always at random moments.

What can that be? Maybe something else is running in the background, or is the game simply poorly optimized? I have already tried to screw down all graphics settings, but to no avail. It lies on the highest settings as well as on low settings. Other games, however, (CSGO and Minecraft) run as usual. I'm starting to despair because I can't play one of my favorite games properly. Does anyone know who else?

Strange and the FPS or the performance in games is rather or mostly from the graphics card then the CPU is in demand. What kind of graphics do you have?

As I said, it is not new:

ATI Radeon HD 5570

Ok new is really not what resolution did you choose because it also draws blatant performance

1920 x 1200

Set that down to 1920x1080 or so low that it's still comfortable

but otherwise I can't think of anything but League is just an esport title, they are always optimized as well as possible, but how much FPS are "usually" because you're talking about break-ins