Matchmaking is the existing automated process in League of Legends that matches a player to and against other players in games.
The system estimates how good a player is based on whom the player beats and to whom the player loses. It tries to make matches where it thinks a player has a 50/50 chance of winning. It knows pre-made teams are an advantage, so it gives pre-made teams tougher opponents than if each player had queued alone (or other premades of a similar total skill level) Riot Games Inc. uses some formulas in an attempt to make the premade teams vs solo players matching fair.
League's matchmaking is largely determined by Matchmaking Rating or MMR. MMR is a number that Riot uses to determine your skill, and when matchmaking, the skill of your opponents. Everyone’s MMR starts at the same point when playing a queue for the first time. It goes up when you win, and goes down when you lose. When looking for games to put you in, it will look for other players whose numbers are close to yours. You have a separate MMR in each queue, so you can climb in one queue without it affecting others.
The basic concept is that the system over time understands how strong of a player you are, and attempts to place you in games with people with similar MMR as much as possible. The game tries to create matches where players have a 50% chance of winning against players who are about the same skill. However, that
League’s matchmaking system puts together a game that tries to balance three things:
- Fair matches - Each team is roughly the same skill
- Position preference - You get to play a position you want to play
- Fast queue times - The time spent queuing is as short as possible
However, it also has to consider multiple factors such as:
- Matches played during low-activity times of day
- Parties of players with very different MMRs
- A shortage of one or more positions (sometimes resulting in one or more players being autofilled)
These are all curveballs the matchmaker has to resolve, forcing it to weigh one aspect more heavily than the others.
To the matchmaker, a “fair” match can be loosely defined as a match in which each team has a 50% +/-1% chance of winning. In a perfect match, ten individuals with identical MMRs queue at the same time, each having selected a unique position that they’re well-suited for. That situation is incredibly rare depending on who is queueing at the time, so sometimes teams can have very slight skill differences (on average, no more than 4-5 MMR).
You must select two preferred positions when entering a draft queue. Your Primary position will be prioritized, with your Secondary as backup. In the event the matchmaker can’t find a full team comp at your skill level, there’s a small chance you will be Autofilled. It’ll trigger if queue times get too long, which is usually because there’s a shortage of one or more positions in the queue - Riot considers this a last resort to get you into a game.
Fast Queue Times
Having fair matches is still a huge priority to ensure League is competitive, but long queue times can be frustrating. Ultimately, Riot would rather you wait a little longer in the queue to get a fairer match, but we know waiting in a queue is probably the least fun part of League. The longer you’re waiting, the matchmaking system may be searching slightly further from your MMR.
The Matchmaking System works along with a modified version of the Elo system. The basic gist of the Elo system is that it uses math to compare two player ratings to guess the game result – like, "Player A will win vs Player B 75% of the time". From there, the game is played. If a player wins, the player gain points. On the contrary, if the player loses, he loses points. If the win was "unexpected" (i.e. the system expects you to lose), the points you gain are larger.
The system was modified for team use, and basically, the concept is that a player gets a team Elo based on whoever is on the team, and if the player wins, it is assumed that everyone on the team was “better” than the guess, and gains points. There are some problems with this, but it generally works out, especially if people use pre-mades a little bit. The System do a few little things to nudge the Elo rating in the right direction when you start out so that people get where they need to get faster.
- Various proprietary methods to identify players that are significantly more skilled than a new player, and boot their rating up a bunch behind the scenes when we notice this.
- Gaining levels boosts a player's Elo rating a lot. This further helps separate level 30 summoners from low level summoners.
Additionally, newer players gain and lose points more rapidly so that they are able to play in their skill level faster. Over time, this means that good players end up high rated because they do better than the system expects, until the system is guessing correctly how often they will win.
Zileas, the VP of game design, has made a detailed post on the matchmaking engine