Now, perhaps, it is clear why it is hard to evaluate individual player skill in Counter-Strike. There are many ways for players to contribute to winning a match. For example, making higher-level tactical choices that increase win probability will not have much of a quantifiable effect on in-game events attributable to that player. But even something as simple as deploying a smokescreen can be hard. A smokescreen that deploys 0.2 radii to the side of where it was meant to go can turn from being an advantage to a disadvantage by giving the opponent concealment rather than obstruction.
Trying to evaluate inidvidual skill has a history going back to at least 2010, when the hltv website launched it’s Rating 1.0. That is based on the observation that the traditional kills-over-deaths ( k/d ) ratio captures 75 % of the variance of game outcome. Practically speaking, the hltv 1.0 rating is a linear combination of the number of kills, deaths, and multikills per round. Notably, it is not at all concerned with progress against objective, because that’s hard to measure. A player could make a negative contribution to their team’s chance of winning, yet do it in a way that gives them a good hltv 1.0 rating.
They tried to fix that with the hltv 2.0 rating. Although it does factor in a variable called impact, it seems to still decompose perfectly into kills and deaths and proxies thereof.
Now we finally get into the Leetify rating. The people at Leetify have, from what I understand, started from a big list of all events (and some combinations of events) that can occur in-game, and based on the historic record of games, estimated how each of those events affect the chances of winning the round.
This means kills can be valued very differently, based on e.g.
If it’s the first kill of the round or happened late in the round. (Early kills are usually more impactful, i.e. change the probability of winning by more.)
If it was against a fully equipped opponent or one that didn’t buy to conserve in-game money for the next round. (Killing a lightly armed opponent usually doesn’t shift the probability of winning by as much as killing a fully equipped one.)
If it was isolated or part of a kill trade (where one player gets a kill but then dies to their opponent’s teammate right after.)
(where one player gets a kill but then dies to their opponent’s teammate right after.) etc.
The Leetify rating of a player is the sum of these changes in win probability from the events attributed to player. In other words, a negative Leetify rating means the player actually reduced their team’s chances of winning compared to if they had run away and hid somewhere on the playing fiend. A positive rating means the player, on average, improved their team’s chances of winning.
Granted, I haven’t looked into many alternatives, but from what I know, the Leetify rating is the best proxy we have for individual player performance.