LATE PSA: If you are having trouble getting S

Play your in URF in a lane which that champion usually never go to(for example, AAtrox is usually played as top or jg, and some rare occasion he could be played mid, so play him bot lane), build full dmg, win the game, then you have a very high chance of getting an S.

Don't ask me how I know this, go spam URF before it's gone.