Patrick McKendry: Why Wayne Barnes' forward pass error really does matter

Rugby referees, like players, coaches and other humans, make mistakes, but those of the professional variety are expected to know the laws of the game, and the most troubling aspect of Wayne Barnes' decision to overrule TJ Perenara's try against Wales was that the Englishman doesn't appear to.

The fact that he missed a forward pass to allow France to beat the All Blacks in their World Cup quarter-final in Cardiff in 2007, for which he will never be forgiven by certain sections of New Zealand's rugby supporting community, is almost a red herring.

In fact, there were probably two forward passes leading up to Yannick Jauzion's try, but Barnes wasn't in line with them (although his assistant was). And this was in the era before television match officials were so prevalent in the game. And, again, mistakes happen - the important thing is that those who make them learn from them.

People saying that Perenara's non-try for the All Blacks against Wales at Eden Park on Saturday didn't affect the game so therefore it's not an issue are also missing the point.

As I said at the start, it's Barnes' job to know the laws.

World Rugby - his employers - have made a comprehensive video, available on YouTube and already featuring comments from rugby fans referring to Barnes' latest mistake, which shows the physics of forward passes.

He should watch it to re-acquaint himself with the law that says a pass is only considered forward when a player's hands move towards the opposition try-line when he or she releases the pass.

The alternative ruling is farcical. On the video there is an elegant illustration of how, under Barnes' ruling, a player throwing the ball back over his or her head to a teammate could be considered to be throwing a forward pass. The ball is moving forward because the players are. It's simple physics.

For Barnes to see Cruden's pass to Perenara several times in slow-motion and to then rule against his TMO George Ayoub, he needed to be in possession of all the facts and on safe ground in terms of the law. In this case, he wasn't, and that's a worry for an international referee.