Referees should show more red and yellow cards in an effort to eradicate dangerous tackles in the game, says World Rugby chief Brett Gosper.
Recent matches have seen controversial challenges, including England’s Owen Farrell’s tackle on South African Andre Esterhuizen, which went unpunished.
The number of reported concussions has risen in each of the last seven years, according to the Rugby Football Union.
“The cards are there to change behaviour,” Gosper said.
He told the Daily Telegraph: “They only continue to be a problem if behaviour does not change. The only way you can get player behaviour to change is to sanction with red cards and actually, we have probably not seen enough of it.”
Gosper says not enough has been done to persuade players to lower the height of the tackle since the law was changed earlier this year and he wants referees to take a tougher stance.
So far this year four leading players – Ireland back Jared Payne, Dragons centre Adam Hughes, La Rochelle lock Jason Eaton and Leicester back-row Dominic Ryan – have been forced to retire as a result of head injuries.
In October, European chiefs vowed to continue the crackdown on contact with the head amid a rash of red and yellow cards being shown this season.
Later that month, Gloucester fly-half Danny Cipriani was given a three-week ban for a high tackle during his side’s Champions Cup defeat by Munster.
In addition, Toulouse back rower Jerome Kaino and Saracens’ Alex Lozowski were given bans of five and four weeks respectively for dangerous tackles.
Farrell’s tackle on Esterhuizen in England’s 12-11 win over South Africa proved pivotal, with the visitors arguing they should have been awarded a late penalty.
The decision not to award a penalty or a card divided opinion among experts on social media.
Gosper added: “I would say in many ways we have probably not been hard enough. There have probably not been as many yellow cards as we would like, and maybe not even as many red cards as we would like.
“We have not had the behaviour change that we are seeking yet, so we have to continue in that vein.”