Please implement something to stop this behavior.
I have INCREASINGLY encountered people who die a few times, flame team for "not helping", then either troll and int or afk in base and continue to flame until the game ends. I am so sick of this happening. It's not difficult to look at a match and determine if someone was griefing or not. I would MUCH rather you put in place some sort of automated ban system for this behavior like you have for chat offenses, and then have to manually unban the few cases that are not intentional griefers.
PS: you also need to start making KDA affect LP gains\losses as well as mmr. Of course, make a minimum so that bad games don't hurt you, but severe cases need to affect your rating. If someone goes 0/9/2 they need to lose 40-50 LP not 15-20.