Play as any character type in a death match or team death match and you'll get this quite quickly you need 8 people includeding yourself to start a Death match or Team death match .
Just keep killing your friends the more health they have that you take away from them the more points your get. For example if you kill someone on full health and do all the damage you will get more points than you would killing someone who is already damaged, this must be a ranked match not player.
This achievement is abit buggy sometimes it will pop in-game and other times after the match has finished.
If you find this solution to be unhelpful, please tell me why in a comment and I will update it the next time I'm online.