Bristol boss Pat Lam says "things have to change" after Siale Piutau was given a three-game ban for punching, claiming he only acted in self defence.

But Lam told BT Sport: "You should be able to defend yourself if someone attacks you like that.

"Siale was attacked by two guys who started swinging at him."

Piutau was sin-binned at the time, while Kitchener was shown a red card for his part in the incident.

But, having seen his side cope comfortably against a much-changed young Northampton side, winning 47-10 on Tuesday, Lam took the chance after the game to reveal just how upset he was at losing Piutau.

He will now not be available to face his old club Wasps on Sunday, Bristol's Premiership play-off rivals, and also misses next week's European Challenge Cup quarter-final with Newport Gwent Dragons.

"Things have got to change," said Lam. "I am just extremely frustrated.

"The messages of inconsistency are what I am struggling with.

"The message that you can start a fight and punch someone with the same penalty.

"The process means he can't strike back. I just think there needs to be clarity and a shake-up."