function PlayerSetup(tParams)
{
    local hPlayer = GetPlayerByUserId(tParams.userid);
    // we assign a think function on the player
    hPlayer.GetOrCreatePrivateScriptScope().Think <- function()
    {
        // get ground entity from netprops
        local hEnt = NetProps.GetPropEntity(self,"m_hGroundEntity");
        // if ground entity is a valid npc
        if (hEnt && hEnt.IsNPC() && hEnt.IsAlive())
        {
            // kill npc
            local dmgInfo = CreateDamageInfo(
                self, null, self.GetOrigin(), self.GetOrigin(), 1e10, DMG_CRUSH);
            hEnt.TakeDamage(dmgInfo);
            DestroyDamageInfo(dmgInfo);
        }
    };
    // run think function
    hPlayer.SetThinkFunction("Think", 0.1);
}
// create a event that triggers when a players joins
ListenToGameEvent("player_join_game", PlayerSetup, "YourContext");