Welsh referee Nigel Owens has revealed officials are aware of players who consistently infringe in the same way, using Ireland' Peter O'Mahony and Conor Murray to emphasise his point.
The Irish back-rower was shown a straight red card early in Ireland's defeat to Wales at the Principality Stadium on Sunday, leaving his team a man down for over an hour.
There were few debates around the decision after he cocked his arm across his chest and connected with Tomas Francis' face whilst recklessly entering a ruck.
Owens described the decision as straightforward for referee Wayne Barnes and pointed out that O'Mahony has previous. He was shown a second yellow card for a similar offence in Munster's last-minute victory over the Scarlets at the start of this season.
"Red cards are never easy and they're not nice to give. Referees don't want to give them unless they have to," Owens told BBC Scrum V.
"But you are there to do the job. It was a pretty straightforward decision really.
"He did it at Parc y Scarlets a few months ago, he got a second yellow card for something similar. He also did it against the Scarlets in the final about four or five years ago, he got a yellow card for something similar.
"I'm not saying Peter O'Mahony is a dirty player one bit but he certainly has a bit of history doing that type of action.
"Players know that you can't go into situations like that, off your feet, leading with the shoulder, forearm or the head.
"That was probably one of the easiest red cards Wayne Barnes will have to give."
When pushed on the issue by former Wales No.8 Scott Quinnell, Owens added: "Personally, I wouldn't go into a game with preconceived ideas but you're aware of what players get sent off, especially some players who have been sent off before for it.
"Something similar happened in the second half when Conor Murray got penalised for blocking the chaser, correctly.
"When we were in a refereeing camp a year or two ago, we actually discussed, from an England v Ireland game, Conor Murray doing that, subtly stepping around and blocking the chasers.
"So when referees do their prep work, they'll be quite aware of these trends that some players and teams do."
Earlier in the show, former Wales fly-half Jonathan Davies was full of praise for George North's performance at 13 and Louis Rees-Zammit's finishing.
"I thought George played well today, I think he's our most dangerous attacker," said Davies.
"He's got to have the ball in hand. He spotted [Iain] Henderson on his inside shoulder, show-and-go and he's gone. That's where [James] Lowe should have stepped in and smashed him.
"Then he got the hands away for the Louis Rees-Zammit try. It was a brilliant finish [by Rees-Zammit], it's an amazing finish and I don't think any other Welshman would have finished that today. He's lightening quick.
"We created two opportunities and we scored two tries but my problem is the lack of creativity inside, [at] 10 and 12."
