Rugby: Physics the answer to forward pass fuss

Dan Carter. Photo / Sarah Ivey

"Law 12: Knock-on or throw forward. Definition: A throw forward occurs when a player throws or passes the ball forward. Forward means towards the opposing team's dead ball line."*

Has there ever been such a fuss about something that reads so simply?

We're not talking about bridging at the breakdown or a tighthead prop boring in on the opposition hooker at scrum time. We're talking about the act of passing the ball via hand from one teammate to another - the very essence of rugby.

Yet nothing has perplexed coaches, commentators, spectators and, yes, referees this Super 15 season as much as the forward pass.

Frustrated referees' boss Lyndon Bray spoke out last week about the Year of the Forward Pass.

To paraphrase, he said: "It's physics - can't you guys get it through your skulls that it's a simple matter of physics."

Or something like that.

The strange thing is that he is right and he's got the experts on his side.

"Basically it's got to be going backwards from the player, faster than the player is running forwards," said professor Matthew Collett, who teaches theoretical physics at the University of Auckland.

"So if the player throws the ball backwards and throws it slower than the speed he is running at, then relative to the ground, the pass will be going forward."

Another way to think about it is to imagine throwing an apple core from a moving car. Try throwing it straight at a fixed point. It is impossible.

The slower the throw, the more it moves relative to the ground and the more it will miss the point you aimed for.

The same principle applies to making a backwards pass while running forward. Where the ball ends up might not be where it's propelled.

So with law 12, the ball was not passed or thrown forward, even though it ended up forward of the point it was released at.

It is the Galilean Transformation in action, obviously.

Signore Galilei has a lot to answer for, including convincing sailors they could pitch their boats off the edge of the world and find their way home via the stars, but his work in deconstructing the forward pass was ahead of his time.

"The velocity in one reference frame is the velocity of the other reference frame plus the relative velocity of the frames," said Collett.

"Here, you're interested in the ball compared to the ground and that's the velocity of the ball compared to the player plus the velocity of the player compared to the ground."

Simple, no?

So maths and science get referees off the hook for a lot of the long passes our uneducated eyes tell us are forward.

What we don't have is a scientific equation that excuses errors off short passes like the one thrown by Will Genia to Ben Tapuai in the Crusaders' galling 16-17 loss to the Reds last month - a loss that looks certain to add thousands more air miles to their Koru Club season.

There is an unscientific equation, however: bad referee positioning + incognisant touch judges + lack of concentration = poor decisions.

* Source: IRB Laws of the Game, Rugby Union 2011.