All leaves are automatically handled by the
LeaverBuster. Leaver Buster is an automated system that Riot implemented to discourage players from leaving League of Legends matches.
Leaving the game during champion selection:
You will receive a punishment (if it wasn't a custom match). On the first offense, you will be unable to join the matchmaking queue for 6 minutes.
For the second and following offenses, you will be unable to join the matchmaking queue for 15 minutes.
In addition to the above time penalties, if the game was a ranked match, you will lose 3 League Points for the first offense and 10LP for the second time before the timer reset.
This timer resets after 8 hours without leaving during champion select and is shared between normal and ranked games.
Leaving the game before the match is over:
A player can leave the game before the match is over. In addition to that, the Leaver Buster system will automatically kick players who remain idle for 5 minutes.
When you leave a game, you will gain no XP/IP for the abandoned game. The match will show up as a
leave in your profile and a
loss is added to your statistics, even if your team wins.
If a game doesn't end (for example for server issues, or because every player left the match), no penalties are given out.
After receiving a certain number of leaves, which varies depending on the total number of games played and the distance in time between each leave, the player account gets first warned and then suspended for increasingly long periods of time, resulting in a permanent ban for re-iterated offenses.
If the majority of the team votes to surrender and the game ends that way, then it's a fair ending of the match. Of course, you will have lost the match and lose LP if it's a ranked game, but it's not considered a leave. You will receive IP and XP for the match.