Team killing is known as killing your own teammates or intentionally making the game hard for them. However, I believe you should not be able to report someone for team killing unless you are the one being team killed. You don't know if the person who team killed someone did it because because they agreed to try and team kill each other. For example, if 2 good players want to try to team kill each other to show whos better, it should be allowed for them to do that as it only gives them a disadvantage in the game.