king-hit 
Australian /NZ informal
noun
A sudden knockout blow.The 30-year-old Williams was outed for 18 matches by the NRL judiciary following his king-hit on Wests Tigers veteran O'Neill at Leichhardt Oval last month....
- The Melbourne forward yesterday had his appeal against an 18-week suspension for a king-hit on O'Neill dismissed by the NRL judiciary chairman.
- What Sunday is expected to claim was a king-hit from behind, Latham told John Laws was ‘a bit of crowd control’.
verb [with object]
Punch (someone) suddenly and hard.That tackle led to Williams king-hitting O'Neill in back play...
- Lawrence was ejected from the pub and then is shown coming back into the pub and king-hitting a bloke who collapsed to the floor.
- Convinced he was about to be king-hit, Banks threw out his forearm.