Players at the 2023 Rugby World Cup would not be able to tackle above the waist if a trial of new laws, aimed at making the sport safer, is successful.
World Rugby will limit tackling to the waist and empower referees to warn players over their tackle technique in selected domestic tournaments.
The laws aim to reduce concussion, the most common injury in Premiership Rugby and a major concern in the game.
If successful, they would be tested globally before France 2023.
"World Rugby is unwavering in its commitment to ensuring rugby is as simple and safe to play as possible for all," said chairman and former England captain Bill Beaumont.
"While injury incidence in the sport is not increasing and concussion incidence is decreasing, we can and must do more to reduce injuries at all levels."
World Rugby's research of more than 1,500 elite-level matches showed that 76% of head injuries occur in the tackle, with the risk of injury more than quadrupling in a "high-contact" tackle compared to a "low-contact" tackle.
However, an experiment that lowered the tackle height from shoulder height to the level of the tackled player's armpit in the second-tier Championship Cup last season had to be abandoned after concussions increased rather than dropped.
While the number of concussions from upright tackles fell, there was a dramatic increase in the number of players suffering concussions in tackles close to the breakdown.
Federations in Australia, France, Georgia, Fiji, Romania and South Africa and have shown interested in implementing some of the experimental laws package in their domestic tournaments, along with the Americas Rugby Championship, a tournament that features the likes of Canada and the United States.
What else is in the laws trials?
- A basketball-style team foul limit that sees the final player to infringe given a yellow card as their team reaches the specific number of penalty or free-kick limit.
- A 50:22 kick giving a team put-in to the line-out if they kick into touch indirectly (ie on the bounce) when kicking either from their own half into the opposition 22m or from inside their own 22m to the opposition half. The law aims to force wingers to drop deep out of the defensive line, creating space for the attacker to run the ball.
- Review of a yellow card during a player's sin-bin period to ensure serious foul play is upgraded to a red card.
- Defending team awarded a drop-out from own tryline when attacking player is held up over the line. The current law is to award an attacking scrum five metres out.
- World Rugby is also considering trials in reducing the number of replacements and a requirement for players to move away from the ball immediately when off their feet at a ruck.