Welcome to SpawnPoint.
First off, if this is the same guy/people each night, try recording a demo and submiting it to
hacker@phxx.com and he'll get added to the perm ban list (if found to be cheating/hacking) if its a different person each time, then use the "report an incident" forum when hes on and you may catch an admin who is around.
Sorry i cant be of much help
Regards,
Michael