In modern rugby, the “thing” in the back of a rugby shirt is usually either a player’s number or, in pro and elite games, a small GPS‑tracking unit sitting in a pocket high between the shoulder blades.

Quick Scoop

1. The obvious part: numbers

On almost all match shirts, the main feature on the back is the large number , which shows the player’s position (1–15 in traditional rugby union, with higher numbers for subs and special roles). Recreational or “fashion” rugby shirts sometimes skip the number, but in organised games it’s almost always there.

2. The mystery “bump” between the shoulders

If you’ve noticed a little rectangular bump high on players’ backs in TV matches, that’s not padding or a design quirk – it’s a GPS tracking device tucked into a special pocket in the shirt.

  • It sits between the shoulder blades in a sewn‑in pouch.
  • In some setups, the device is instead held in a tight chest harness that looks like a sports bra, with the bump still visible under the jersey.

These units don’t just track where a player runs. They typically combine:

  • GPS (how far and how fast they run).
  • Accelerometers and gyroscopes (how hard they accelerate, decelerate, or get hit).
  • Sometimes extra sensors for heart rate and other load metrics.

Coaches and medical teams then use that data to:

  • Monitor total distance, high‑speed sprints, and work rate.
  • Measure impact forces in tackles to help manage head‑impact and fatigue risk.
  • Adjust training loads and tactics based on how hard different positions are working.

3. Why this became standard

Over the last decade or so, GPS units have become standard in top‑level rugby, to the point that many pro jerseys are now designed with a built‑in pocket at the top of the back just for the device.

  • Earlier on, teams sometimes kept the units in shorts pouches or separate harnesses.
  • As the benefits became clear (better data, safer monitoring), kit manufacturers integrated that pocket directly into the shirt.

4. If you’re just buying a fan or club shirt

For fan replica shirts or lower‑level club jerseys:

  • You’ll usually have: number on the back, plus name and sponsor logos depending on the competition.
  • You may or may not have a GPS pocket; it’s more common in pro‑level or “player issue” shirts.
  • Most amateur players will only wear a GPS unit if the club invests in tracking tech – otherwise their backs just show the number and design.

5. Tiny story to picture it

Imagine a flanker in a modern international: from the stands you see just a tight shirt with “7” and a small rectangle pushing the fabric out behind his neck. Inside that little bump is a whole mini‑lab quietly logging every sprint, sidestep, and collision, so that when he comes off the field, the coach already knows exactly how hard his body has worked that day.

TL;DR: The back of a rugby shirt mainly has the player’s number , and in professional rugby there’s often a small GPS‑tracking unit in a pocket between the shoulder blades that collects performance and impact data.

Information gathered from public forums or data available on the internet and portrayed here.