A stomp and a punch has marred the final seconds of a top schoolboy rugby match, and a Christchurch Boys' High School hooker red-carded for the double acts of foul play.

The ugly incident unfolded as Napier Boys' High School romped to a 31-12 victory over their southern rivals in the National Top Four semifinal in Palmerston North yesterday.

Footage of the incident shows a Christchurch Boys' High School's reserve hooker stomping on an opponent's head during the breakdown.

The same player then punches another player in the push and shove that developed after the incident.

The match referee red-carded the player, telling his captain: "He needs to understand he can't do that".

Napier Boys' were awarded the Moascar Cup - the Ranfurly Shield of New Zealand Secondary Schools rugby - and will now turn their attention to the National Top Four title.

The team take on St Peter's College of Auckland in tomorrow's boys' final at the Sport and Rugby Institute in Palmerston North.

The girls' final will be contested by Palmerston North's Manukura and Hamilton Girls' High School and the co-ed final between Rangiora High School and St Peter's Cambridge.