Two melee assholes did this to me in NA DTV just a little while ago. I was trying to setup to shoot at the waves as they appeared. Time and again, for whatever douchebag reason they had, they'd surround me and wait for me to keep getting knocked down from touching them or nudging me, and let me die to the mobs, then fight. So, anyone can grief any allied ranged character they want into leaving, essentially, any server they want.
Reporting one person for that could take as much as five 3 wave rounds. Reporting more is stupid hard, because if they time two knockdowns close enough, and you're trying to play, not focus on reporting griefers, they can ensure you're screwed and only get one report between them. The report only works on the last person to have done anything.
Games should be fun, not give people license to completely waste others' time.