Referee Nigel Owens says the red card given to Scotland's Zander Fagerson at Murrayfield on Saturday was "as clear as you could see".
The prop was handed his marching orders in the 53rd minute of the Six Nations clash after he cleared out Wales' Wyn Jones.
The forward caught Jones with his head, and, running from distance and leading with the shoulder, it was judged it to be a sending-off offence.
Giving Fagerson his marching orders, referee Matthew Carley said: "You've had a clear line of sight and you've hit him directly in the head."
It is the second time Wales have ended up playing against 14 men in the space of six days, with Ireland's Peter O'Mahony sent off early at the Principality Stadium last weekend.
Like the O'Mahony incident, the Fagerson decision prompted plenty of debate between fans and former players, but former Test referee Owens - in his Daily Mail column - says it was a clear-cut decision.
He said: "The red card shown to Scotland prop Zander Fagerson in the Wales game was as clear as you could see.
"He ran in from distance, with his arm tucked in by his side. He came in off his feet and led with his shoulder straight to the head of Wyn Jones. There was no attempt to enter the ruck with his arms out. No attempt to bind. No control.
"It is a clear red card. No one should defend that. We don't want to see that in the game.
"People will have their opinions but if they think that something like that is okay, I'm sorry, but they need to have a good think about the type of game we want to see."
Owens also took his point onto social media, replying to a tweet from former Wales player Lee Jarvis.
Owens also offered his view on the conduct of England captain Owen Farrell against Italy at Twickenham.
Farrell's challenge on Italy scrum-half Stephen Varney saw him come under fire, with the England centre hitting the Italian from behind with no arms.
After some deliberation with the TMO, no action was taken against Farrell, but it was his on-field manner which Owens focused on in his column.
He believes that Farrell should cut down on the chat with referees, adding that he himself has never had any issues with the England captain.
"He is a great guy both on and off the field", he wrote. "But there was too much chat from him to the referee. That must stop.
"He never did that with me. Every time I referee, I tell the players that there is a time and a place for conversation. If they want to discuss something, they have to do it in the right manner. That is one of the game's values.
"I never have any issues with Owen. Whenever I reffed him, he was always polite. He knew where the line was and never crossed it.
"That shows he can do it. It is up to the referees to keep strong and stay on top of things like that.
"I think he was also fortunate not to be penalised for his late hit on the Italy scrum-half. No doubt about it. He knows the ball has been passed and he followed through to let him know he was there.
"It's a penalty so England's try that followed should not have stood. Add that to Jonny May's, which should have been disallowed, and I think England were lucky on two occasions."
