The rectangular lump on the back of rugby shirts is a GPS tracking device that provides detailed performance data. The device is inserted into a specially made pocket on the back of the shirt or carried in a harness worn under the shirt. The GPS tracker measures a variety of physical data emitted by the player, including distance covered, speeds reached, and overall heart rate. The device is designed to sustain collisions and scrums. The data collected by the GPS tracker can help coaches and analysts gather information on how much ground a player has covered, at what speeds, and when a players intensity starts to drop. The GPS tracker is an important piece of kit that is used by many elite club and country rugby teams.