How many games of feeding does it take to have Riot ban?

Hey guys! I played a game of lol last night and i came across a REAL intentional feeder. In champselect this guy was my support and picked amumu. As soon as we spawned in game he marched down mid lane and took 2 tower hits and gave fizz first blood. Ok.... my team was really confused because I think in our life of playing league of legends this was the first time we encountered an intentional feeder. When Amumu spawned he went down mid lane again and again and again and again until Fizz was so fed that we couldnt take him down. Crazy part is that the enemy team didn't even care about what was going on. They all chatted Amumu to come to their lanes so they can get fed. Amumu didn't say a word in the game. i don't know if this was a bot playing but he would ult randomly. Pop ghost and heal and bot items. After this loss I lolking-ed him and found out that Amumu has been doing this every single game and took innocent summoner's LPs. So my question is: how long does it take to have Riot ban a legit intentional feeder?

Here is the lolking: [(http://www.lolking.net/summoner/na/74641315#matches)]