Things that don't give an S
Single handedly carrying your team (more than twice anyone else's kills) Perfect KDA Having ALL tower destroys on your team Being on a huge killing spree Earning the most gold in the game
How do I know this? Manged all of these things in one game and got a A+.
Something that might be related to getting an S: Being the highest lvl at the end of the game. Ryze, who earned an S in that very same game was 2 lvls above me despite only 2 more cs, 8 less kills, and no objective contribution.