So, recently I've been having this issue. I'll play a champ until lvl 5 mastery, getting loads of S's along the way. Then once I hit lvl 5 mastery, I can only get A+. What constitutes an S? Also, does it get harder at mastery lvl 5? Thanks in advance guys. [slayer-jinx-wink]
It doesn't get harder depending on your previous performances - but if a champion performs better throught different patches, it can make it somewhat harder because the average performance for that champion increases slightly and therefore the requirement for better grades. Everything that is taken into account is compared to the performance of other players with the same champion:
You may add other factors here
Riot officially stated that they're not giving away the formula on how score works. The only think they've shared is that it's based on other players who play the same champion in similar elo range, and that for supports, kills and assists have the same weight, so by extension this would mean that kills have more weight than assists on all other positions. That said, a lot of players speculate from experience that CS is a huge part of what score you get.
Also, does it get harder at mastery lvl 5? Thanks in advance guys.
In theory no, it should be the same.
And in my experience I haven't noticed that is harder to get S once I reach M5, for me it feels the same.
A donkey.
Were you playing the same champ for both of those games? Because that can change things. What's an S score for one champ might not be for another because people play them at varying skill levels. Even if it was the same champ, depending on how far apart the games were could have changed it because people's average skill/score with them may have changed due to a patch/buff/nerf/etc.
At the end of the day there's no way for us to tell you what you have to get in order to get an S on a champion, because only Riot knows that and they're not telling us. I've ended games with a better kda ratio than people who get an S in that game but I only get a B at best. It's just a fun little thing that we can't predict unfortunately.
What I do know is that people have said playing a champ outside of their usual role tends to help, because people won't usually do it so a positive score with few deaths ought to get you an S. For example, playing Veigar support instead of mid, which is how I got my S rank with him for this season's chest.
Just random luck I guess, I played ornn stomped many times my lane, got a decent farm and many assists - no S. then I played one time Ornn support - S+. WHUT?
Most guys say it's not just necessary to have a good KDA, you also need a good farm - pretty hard to farm - when your team always needs your help cuz of this meta where you teamfight the 10/15 min mark....
Always be making big plays. At least that works for me at least.
Well riot has stated that they won't reveal the formula for an S. From my personal experience CS has a huge role in it (Not for supports tho) Champion difficulty (and potentially winrate) also matter. For example I've gotten an S on Azir with an average KDA of 4-2-3 (this is a 'good' KDA for Azir however) and good CSing. If you playing a relatively easy carry champion than you have to work much harder.
Get loads of farm and a half decent score and you are guaranteed an S. I have noticed the mastery system really only cares about farm.
I still think CS playing a factor in score for anyone not a mage/adc is rubbish. ESPECIALLY in a mode like ARAM, where no one BUT the mage/ADC is going to get CS.
Unless you see Xerath not waveclearing so Mundo can get three creeps while being fired upon.
I appreciate you guys' quick response! So I'm going to see if I can throw some stats in to help. So this last game I went 11/2/5 with 144 farm for 23 minutes being in the game with a vision score of 38. That's a kill participation of 16/28, that's about a 57% kill participation. Farm is roughly 6.2 per min (I know "perfect" farm is 10 per minute but I was ganking other lanes a bit too much I think.) I received an A+ for this game.
By comparison, I had a game where I went 16/6/7 with 204 farm for 33 minutes being in the game with a vision score of 58. Kill participation of 23/44 which is 52% kill participation. Farm is roughly 6.2 again and I received an S for this game. So, these games are really close together in stats. Maybe it's just because I got more kills? I'm just kinda confused on what the stipulations are for gaining an S.
Kill participation, Objective participation, Vision score, KDA.
On all except farm will make the difference between A+ and S 99% of the time.
basically its just cs
The biggest factor I have seen is cs. To answer your question though it is a combination of cs, deaths, kills, vision, objective participation, and assists in the role you are playing compared to other people playing the same champ in the same role. SO if you play something off meta and do well you will more likely get an S. Like master yi top or jungle teemo.
It takes your statistics from the game and compares them to the average [being B+?] ones.
If you perform a lot better in a role on a champion than the average player, you'll get an S, if you perform from the top 0.1-5% you'll get an S+
It also takes into account time spent in the game.
So having a 5-0-3 75 cs, 30 vision score, score on 
might be an S- for a 12 minute game, but for a 50 minute one that would be a B- or a C even.
I believe part of the equation for what you get assigned is other players doing good around you as well, not just how people play on the champion. I've done really good in some games and hit that A+ threshold where I felt I should have got an S, and then hit a similar score at another point in time, and get an S when my team did way worse. It seems like "carrying" gives you positive results when it comes to that kind of thing. I'm not entirely sure how all of that adds up but that is the pattern I see. If one person is getting 10+ kills, while everyone is getting less than 4, usually they'll get an S, but if multiple people on the team get lots of kills, unless it's a huge amount with no deaths. Seems like it's rare for there to be multiple S's popping.
I've seen one game where multiple got S with high scores, and they all had 0 deaths. Again this is all just speculation from what I've seen, but I think how your performance as a team is evaluated goes into it as well.
