So i played this game, I was veigar mid, got 11/2/5, and my teammate was akali top, with 7/7/12, she got an S- while i got an A, I mean how? 😂 How are ranks given in league?? Game link matchhistory.eune.leagueoflegends.com/en/#match-details/EUN1/141521699/221322001?tab=overview
Mastery grades depend on your percentile performance relative to all other players on that particular champ in that particular role.
Those in others roles and on different champions have no influence on your grade, and only the performances on the same champ in the same role are comparable. There no absolute requirements, just how to compare to others, so if you play a champ/role combo that everyone does horrible on, and you do slightly less horrible (but still 'bad' by most absolute standards) it's quite possible to get an S+. That said, theres mains for pretty much every champ/role combo, so you generally still have to do reasonably good. Some champ/role combinations require you to be really good though.
What mystic said, but also it isn't just your KD. It's other factors too such as CS. When I used to main Veigar, it was common to go crazy KDAs and other factors, so unfortunately you'll have to do a lot to get an S :(
