Board Thread:League of Legends discussion/@comment-24921749-20140509155236/@comment-3308937-20140509161904

Freddamonster wrote: he gets a ban once twice three times and then gets permanently banned.

That's not how it works. If you want to discuss something please read up on easily available information regarding the subject.

How long can I get banned for?

The Leaver Buster system issues bans between 1 hour and 7 days depending on your Leaver Level. As the number of leaves against your account increases, you will receive harsher penalties that could culminate in the permanent suspension of your League of Legends account. The system periodically issues permanent bans against accounts that have hit the 7 day ban too many times.

https://support.leagueoflegends.com/entries/20030633-Leaving-Games-The-Leaver-Buster-FAQ:

So they have to climb the ladder from 1 hour to 7 days which could be like 5+ different bans right there and then have to receive that 7 day ban multiple times and still keep leaving to have their account permabanned by the leaverbuster.

Obviously someone doesn't care too much about their account or all their time invested if they're going to completely ignore the mass "warning" bans they're receiving.