How does the punishment system work?

Hi!

So I was just wondering if somebody ints your game, then ragequits (even stating it in chat), and I report him, how can he NOT get punished? Later he confirmed it in private chat too. So how does this system work, can you do more than reporting him, since it looks like it doesn't matter.

btw yasuo from my last game. He has only 5 deaths bc he left game before end (even said it in chat).

Thanks for your help!