Kill Steal
"Kill Steal", or killing a monster which doesn't belong to the player, (Someone else/some other party is attempting to kill it or the monster is attacking them) is a bannable offense, and very poor manners. Don't do it!
Gravity Interactive (and an the NyanRO Team) officially categorizes Kill Stealing under Harassment. It is not uncommon for mistakes to happen, and there is a threshold for determining if a behavior was harassment/KSing. A single incident where someone comes up and takes a whack or two at your monster is NOT KSing. A person who makes a habit of attacking your monsters IS KSing. To successfully report an incident of KSing you need to include screenshots of the offender attacking your monsters on a few different occasions. You should also try and have before and during screenshots so that the GMs can clearly see that the offender was attacking YOUR monster.
Not all monsters fall under the no-Kill Stealing rule. MVPs and player-summoned monsters are considered Free for All.
You can also use the .noks command ingame to avoid KSing.