Rule 11

11) No-PKs are not allowed to interfere in PK battles directly.
   
   NO-PK players may not act in a beneficial or detrimental manner
towards PK players during PK battles.  'During' is defined as the time the
pk timer is activated.  The only time a NO-PK may assist a PK player is in 
the ARENA, or while their pk timer is inactive.  You are responsible for 
using some common sense in determining if someone's timer is active.
'Accidents' may still get you punished, depending on the situation.

(See also: CLAN, RULES, 'PK RULES', ARENA.)