Sooo, i was running around in Free-for-All and i see the feed is showing one guy knifing the same dude over and over, so i just decided to look for them and i foudn them hiding in a corner with a tactical insertion. I killed the knifer on his 23rd kill, then the dude and took him out after he respawned.
Stupid fags, dont play the game if you need to cheat to get kills.