'I don't understand it': Dave Rennie frustrated with Northern Hemisphere powers

Wallabies coach Dave Rennie has raised an eyebrow at Northern Hemisphere rugby nations for thwarting attempts to introduce a 20-minute red card replacement rule in tests later this year.

World Rugby is set to trial both the 50-22 and goal-line drop-out rules that were Rugby Australia initiatives for the Super Rugby AU and Trans-Tasman seasons.

The August 1 introduction of the laws will see the Wallabies play under a different set of laws against France in July than they will against New Zealand, South Africa and Argentina in The Rugby Championship.

A team will earn the lineout throw if they kick from inside their own half and find touch inside their opponent's 22 - or from inside their 22 into the opponent's half.

The other change will see the defending team take a goal-line drop-out rather than defend a close-range scrum - if the attacker is held up over the line.

Rennie is a fan of both rule changes, with the 50-22 variation potentially opening up the field for more expansive attack and the drop-out speeding up play and avoiding a "bit of volleyball" by handing possession back to a team in threatening field position.

But he is adamant the ability to replace a red-carded player after 20 minutes - the other Rugby Australia initiative trialled in Super Rugby AU - should also be in play.

"It had enormous support in the Southern Hemisphere, but not the Northern (France and England) and I'm not sure (why), I don't understand it," he said.

"Some decisions are made that have a massive impact on a game and maybe post-game are viewed as not as serious.

"At least at 20 minutes you can even the numbers up again."

Last November, Australia beat New Zealand in a test that ended 14-a-side when Ofa Tu'ungafasi and Lachie Swinton were both red-carded for dangerous tackles.

"As we know there's a lot of emphasis around head contact, there's going to be a lot of cards," Rennie said.

"Individuals who get it wrong are going to be punished. They will spend a long time on the sidelines but if we can get back to 15 on 15 that's what we want."

- Murray Wenzel