who determines this grading,

Use your Print Screen key to get a screenshot... If you're on Windows, you can capture just the active window by pressing Windows Key + Alt + Print Screen. You could use something like Gyazo to easily do it too.

Anyway, the grade is based on your performance compared to others on your champ in that role. Your CS might have been too low per minute, gold, deaths, all kinds of factors, but in the end it's simply you compared to the rest.

My guess its like a score list Someone must have outdone your scores by several games If you play that champ in another role you get better scores?

what am i looking at?