Rugby’s “unseen work” is a term that can be bandied about during rugby commentary. It’s usually spoken of with regard to forwards, particularly the grizzled chaps who shun the bright lights of ‘carries’ or ‘metres made’ to instead concentrate on applying themselves to dark arts in dark places.

At Twickenham in the 2014 Six Nations, Leinster's Jordi Murphy came on for starting openside Chris Henry in the 71st minute. Murphy would end that substitute appearance with zero carries, zero tackles. An ineffective substitute outing?

In any ball game the observer’s eye is naturally drawn to the object of desire at the centre of proceedings. Understandably when people started recording stats they concentrated on the ball, counting and recording the action directly around it. Tackles made (and missed), carries, kicks, metres made with ball in hand. These are the stats that get onto the screens. Easy to see, and count, because they’re all on-the-ball actions.

Prozone, mostly known for their stats-gathering work in soccer, are now back in the rugby game.

One particular card they bring to the table is recording what happens around the breakdown area. The tackle is made – what happens then?

When watching either live or from the sofa, one sees a swarm of jerseys pile in to try to either secure or steal the ball. Prozone measure this. It’s called ‘breakdown arrivals’, and it goes a long way to shine a light on some of rugby’s dark matter.

On the surface, the concepts behind Prozone’s breakdown arrival data are simple. It’s just counting: people and time. After a tackle, count the first three arrivals to a breakdown and put a tick against each name. At the same time, measure the amount of time it takes for the attacking team to recycle the ball. After the match, add up all a player’s ticks. Then calculate the average time each team took to recycle the ball.

To illustrate, in Ireland's 28-6 victory against Scotland in last season's Six Nations opener, Ireland took the ball into 115 rucks. Of these, openside flanker Henry was within the first three arrivals 31 times. Next best for Ireland were Dan Tuohy and Jamie Heaslip. Nothing too surprising there, perhaps. And they all got into double figures in either tackles or carries, stats that we're used to seeing on screen or in the newspaper.

But then the eye drops down the list to the backs, and Andrew Trimble.

Trimble scored a try that day. He was in the middle of an outstanding season for both province and country. But his six tackles and just three carries would not have stood out on the TV post-game stats sheet. However, he led all Irish backs by some distance in being in the first three to Irish rucks 17 times. Support work, unglamorous and unseen. And hugely valuable in a team built around a ruck-centred gameplan.

Rugby has changed significantly over the years. There are fewer set pieces and far more rucks, meaning control of that breakdown area is crucial. Joe Schmidt has set his stall out in this area as Ireland coach, shunning offloads in favour of speedy clearout and ball presentation at the breakdown.

Ireland’s average ruck recycle time in that game was three seconds, beating Scotland’s 3.6 seconds. Game two? Ireland’s 3.2 seconds to Wales’ 3.3. It was a trend that would continue throughout the 2014 championship.

All this is nothing new to a professional team’s analyst. They’ll go into far more detail, taking into account factors such as ball presentation quality, clearout technique, even the decision to engage with the ruck itself.

Some of that can be judged from outside; some cannot. For example, on occasion a team might not want quick ruck speed depending on who was in the ruck, who was lined up outside at first receiver or even the line speed of the defensive line on that day.

“Predominantly, the seven is going to get to the most rucks in a game”, said Leinster flanker Shane Jennings. “So, in terms of numbers – let’s say he’s hitting 30-plus rucks or 20-plus rucks – then you’ve got to see how effective he is. You can hit a ruck and be ineffective, which is pretty pointless.”

This echoed the thoughts of a number of team analysts, one of whom said “it is no good hitting 40 rucks if you’re just standing at the back inspecting”.

In terms of ruck quality, Jennings emphasised the importance of the ball carrier’s effectiveness in the carry, getting onto the ground and placing the ball well. After the ball carrier “the first arrival is the key”, said Jennings, “because if the first arrival doesn’t do his job, it’s over”.

That first arrival might not always engage in the ruck. “The assist tackler also has a decision to make whether he contests the ball, tries to take the space past the ball or whether he leaves the ruck and waits for a better chance of success”, said Grenoble head coach Bernard Jackman. “For example, if a back is their first support I would give my players more leeway to attack the ruck. Obviously the number of support players they have around the ball and their distance from the tackle point are also important triggers, as is the area of the pitch, the score and time on the clock”.

Jackman said at Grenoble they target a success rate of over 90 per cent where their first clearout player arrives before the opposition’s assist tackler.

That spring day in Twickenham the Irish and English analysts will have noted that Jordi Murphy, while without a single carry or tackle, was one of the first three arrivals to 10 breakdowns in just nine minutes on the field.

With Prozone’s ruck data perhaps now others can have at least a small glimpse of rugby’s unseen work.