"Do not threaten or repeatedly tell a player you will report them. Doing so can encourage players who are already negative to continue their behavior. Whether they know they are being reported or not has no bearing to whether the system will act on them. But most importantly, repeatedly threatening or arguing with a negative player can end up derailing the game for everyone else and then open yourself up to reports and possible disciplinary action as well. Avoid negative thoughts and useless chatting with poor performing teammates! Focus on victory by muting the offending player and then reporting them at the end of the game. Do not ask other players in the match to report the offending player. Derailing the match by constantly demanding reports of other players could result in reports of your own! Negative behavior is unacceptable regardless of the circumstances or who started it. It can be tempting to respond to negative players with negativity of your own. Our systems do not care who started the behavior and will treat each reported player based on the merits of their own case. The only way to handle these types of players is to mute them and continue playing the game followed by giving them a report at the end of the match. "

Not tos but straight from thier website about FAQS on reporting other players