The opening round of Super Rugby provoked some comparisons with the Six Nations and calls to amend the replacement rule.

Those picking apart the churning style in the Six Nations should remember the mistake-laden Lions-Sunwolves game and the limp production from the Hurricanes. Nothing much to laud there.

Early season struggles? Maybe. Average set-piece quality? Got a point there. Holes in the playing rosters? Could be the go.

It doesn't stop teams emptying their benches around the hour mark and that pattern is messing with the shape of the game. It's rare for a match to end with any subs left on the bench but that can provoke dramas as the Crusaders discovered.

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When they subbed Tim Boys he was unable to return for his replacement Reed Prinsep who was knocked out soon after.

Listen: Steven Luatua talks to the Crowd Goes Wild Breakfast ahead of the side's next match against the Crusaders

Games are 23-man contests with coaches permitted to tinker with any combination on their eight-man bench. Then the Crusaders still bleated they did not have enough cover when they ran into their late mishaps.

That was certainly unfortunate but is one of the hazards for coaches as they take a punt switching players or sit on their hands.

We hear coaches talk about the similarities between the 23 players they choose and each game is geared towards those extended numbers.

Rugby should allow unlimited interchange or restrict the use of reserves so matches break open as players tire and the defensive overloads ease. Eight rolling subs or a handful of judicious choices?