"NLR" Is when once you die, you can not step inside the district or tunnel connected to the district, of which you died in, if you do not abide by this, that would be you breaking nlr.
Also you can not ask the player that killed you why he killed you.

I would ask player y why he killed player x. If he does not respond, i would warn him. If he says that it was due to a hit, i would tell him to show me proof of the hit, or i would look for the hit in which player x was killed from, myself. If there is no proof of the hit, he would be warned. If player y said it was due to him stepping inside his base, i would ask player x if he had any proof of himself being killed not inside the base. If player x fails to provide proof, i would let them both go without any punishment.