I've seen this crop up on the boards quite a few times where people claim they got banned for defending themselves from trolls/flamers/premades/etc. I can assure you that this is not the case. I want to explain the difference. Let me start off by stating a few things.
1) I have been playing since the beginning of season 3. I have thousands of games under my belt. I've played enough to have every single champ unlocked and 20 rune pages. I have ***never*** had ***any*** form of punishment on my account. No bans, no chat restrictions, not even a warning.
2) This post will contain strong language. This is a warning. That being said, its nothing you haven't already heard while playing LoL or just using the internet in general.
* **"So Eedat, how do you deal with these people and not get banned?"**
Well when I have a straight up troll/feeder on my team, I tend to tell them "stop being a douche" or "what an asshole" or maybe even a good old "fuck off". I say I do this to a good 80% of the ones I encounter. The other 20% are the ones I think are just heavily tilted and can be brought back.
* # !!??!!?!?!?!?! "BUT WHY DONT YOU GET BANNED WHEN I DID?!? YOU FLAMED THEM!!!"
You see, here is the difference. After I say one thing to them, I mute them. I do not acknowledge them ever again. The difference between me and you is that you continued to berate them the entire game. You didnt stop at just saying one thing. You spent the next twenty minutes typing paragraphs of insults. Instead of dealing with the flamer, you became one yourself. You lowered yourself to the same level as them and therefore will be punished as such.
Instead of muting them like I do, you decided to to take time out of the rest of the game to call them a "worthless pos", "garbage feeder", "waste of life", "/all report x9 this bitch", etc. Maybe you even really lost it and told them "kys". Your lack of self control is what got you banned.
That being said, I will concede the way I deal with them technically is considered toxic. Here's the thing that most people dont understand. Unless you go off and say something to get automatically flagged (I.E. kys, homophobic/racial slurs, etc), there is a real person that reviews the case. They will see that 0/14/2 feeder that is flaming everyone then see my ***ONE*** comment and most likely give me a low toxicity rating, if any at all, because I limited it to just one response. These Rioters are actual people that can make sense of a situation and dont just look at the one line I said and nothing else. They aren't some heartless drone that is incapable of relating.
This is another scenario I would like to address that I see a lot. I see someone either actively or passive aggressively antagonizes a player until the person loses their cool and snaps back. Do you actively provoke your teammates by doing stuff like walking into their lane to take their farm for no reason or stealing away a jungle camp they were clearing? Do you drop passive-aggressive comments like "top has 60 farm at 20 minutes lol" or "our bot lane is 0/5" or "not worth trying to help this mid"? Although ***technically*** you could just be stating a fact, we all know the only reason you're pointing it out is to antagonize them. Do you then use them snapping back as an excuse to "defend yourself"? I hate to be the bearer of bad news, but you deserved your ban. That isnt "defending myself". ***You actively set up the situation.*** You went out of your way to bait an aggressive response. Dont pretend to be an angel thats free of fault. We arent children that are incapable of seeing what you did.
* **"But why doesnt the other person get banned too then?!?!??!"**
They are guilty, just as you are. The difference is if they behave in all their other games and only lost their cool in one game out of the last 50, they wont get a ban. If they don't, they are eligible for punishment as well. You, on the other hand, probably do this quite frequently for the sake of "self-defense". That is why you got banned and they didnt.
To summarize, dont spend the entire game flaming a feeder/troll or dont actively bait out aggression for an excuse to "defend myself" and you won't get banned. If you fail to do so, dont be surprised by the consequences.
Best of luck to you on the Rift.