How does the report system in League of Legends work?

There is no set number of reports that automatically determines whether or not you will come before the Tribunal.

In section 14 of the Tribunal FAQ, you'll find the information that addresses your question.

I just got reported. Does this mean I will be reviewed by the Tribunal?

It depends, but not necessarily. Players are only reviewed by the Tribunal if there is significant evidence to support a need for their behavior to be reviewed. Our system takes a variety of factors into account as player reports roll in, so simply getting reported once is unlikely to land you in front of the Tribunal. Here are a few of the factors considered before you find yourself on the docket:

• Accounts that accrue a large volume of player reports are much more likely to be reviewed.
• New accounts are judged more stringently than veterans.
• The reputation of the player who is reporting you will also be taken into account. Reports made by level 30 summoners with clean record will be weighed more heavily than those submitted by newer accounts and/or those whose reputation has been tarnished by frequent harassment reports.

As you can see, there are a number of factors that go into Tribunal reports, and this is not the full list, as Riot does not disclose that. The linked FAQ should be able to answer any other questions that you have about the Tribunal process.

I can't tell you exact number but this is how it seems to work. Let's say you were mad and started feeding so 3 members of your team and 2 of the other reported you. That wouldn't do much, but get you headed on your way to the tribunal. Now if you did it again and people reported you again then you'd probably be sent to the tribunal where the user base decides on if you should be punished or not. Depending on the chat logs and what the users said that reported you. You could receive a temp ban, perma ban, or just a warning. If this keeps going it will lead to a perma ban.

One exception to the reporting system is the "Bad Player/Noob" Report option. Riot has said that they will not punish anyone for being bad. Reporting anyone with that option does nothing. So if they are reporting you for being bad, don't worry about account bans. But do try to get better as it's more fun if you are winning. Good luck on the rift!

A detailed video can be found here:

Its presented by Riot on how the whole system works, and the reasons why they chose it, it's pretty lengthy and overkill for the information you need.