Ubisoft is trialling a new player reporting system in Rainbow Six Siege in an attempt to stomp out "toxic behaviour" in the game. The system is only active in the technical test server for now, and for a user to be banned you'll have to provide definitive proof that they're behaving badly.
It's not fully clear what constitutes "toxic behaviour": the game's code of conduct lists things like harassment, discriminatory language and spamming in chat. But I reckon you can probably add teamkilling to that list too—it's something that Ubisoft is determined to crack down on, and last week it revealed it was considering removing friendly fire in casual playlists to do just that.
Ubisoft is not introducing automatic ban sanctions "so no one will get trolled into a ban", and you'll have to submit proof such as chat logs, videos and screenshots for the publisher to take action against a particular player.
Justin Kruger, a community developer at Ubisoft, promised more information about how the system works soon. As long as the team acts on evidence that players provide, then I think this is a step forward.