The rugby GPS conversation generally runs something like this. 

“What’s that rectangular lump on the back of professional rugby players’ shirts?” a relative newcomer to the game may ask.

“That’s their GPS tracker,” comes the knowledgeable response. And, there, the conversation ends, with a certain amount of nodding and no further enlightenment on either side.

And, it’s wrong. Well, nearly. Yes, it’s a GPS tracker. But it’s not just a GPS tracker. It’s also a gyroscope, an accelerometer, and a magnetometer. It may also have a heart-rate monitor. And there’s also a transmitter that sends all the data to coaches’ and analysts’ computers in real time.

It’s an important piece of kit – which is why players are seen these days carefully removing them before they swap shirts.

Related: Opinion: Rugby needs more technology, not less

Professional rugby shirts frequently contain a special pocket, at the top of the back, for the device to be inserted. Otherwise, players may wear a special chest-hugging harness that’s sometimes known as a sports bra.

They came to rugby in the early 2000s via Leinster Rugby. Then-coach Michael Cheika had seen them used in Australian Rules Football, and started using them in training. Today, they’re pretty much ubiquitous in elite club and country rugby

But how do they work?

GPS

We all know about GPS – it’s on our mobile phones, and in modern cars’ computers. It tells us where we are, and helps us get where we need to be. Let’s be honest, where would we be without it, these days?

(Other satellite tracking systems are available. GPS is the one owned by the US government that, like Hoover, or Google, Taser, and Xerox, has almost become a generic term.)

For rugby purposes, the GPS tracker – and GPS is commonly used – allows coaches and analysts to gather date on how much ground a player has covered, at what speeds and the lines they run as play unfolds.

Accelerometer, gyroscope and magnetometer

In fairness, the GPS part of the little black box in players’ sports bras gathers most of the data. But not all of it. 

Rugby players make tackles. Some rugby players make a lot of tackles. And that’s where the three other instruments in the GPS tracker come in.

The accelerometer delivers information on sudden changes in force caused, for example, when a player is tackled or makes a tackle, or when they join a ruck. 

The data from the accelerometer is pretty basic, giving data on changes in speed and force only. This is where the gyroscope and magnetometer come in. They supply additional information on directional changes that help coaches and analysts understand how tackles and rucks are affecting their players’ bodies.

Heart monitor

Sometimes it’s in the GPS tracking device that’s not just a GPS tracking device. Sometimes it’s on a separate harness, but it’s still worth mentioning. 

It does what it says it does. And that helps coaches monitor players’ fatigue levels. And that helps them determine whether that player needs subbing off during a game, or whether they need to work harder in training.

Put all this information together, and coaches have data-driven information on their players to add to the ‘evidence of their own eyes’ from what they’re seeing on the pitch.

This allows them, in turn, to substitute players who have gassed themselves before it is too late and they have picked up an avoidable injury or have conceded a try.

They can also be used in training to ensure players are in peak conditions so that they’re ready to go whenever they’re called up to the matchday squad. 

It may indicate why certain players aren’t performing as expected – backs not hitting their top speed as quickly as the had been doing may be a training issue that needs rectifying

Tactics

As well as health and fitness, trackers can also be a tactical tool. They show where players are at a given time, which means coaches can look at planned moves and understand exactly why they work. Or don’t. And then they can make adjustments as necessary.

So, rugby’s ‘GPS tracker’ … In a game that is increasingly reliant on real-time data, it’s another multi-faceted tool in coaching teams’ armoury. 

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