The square patch on the back of a rugby shirt is a visible part of a sophisticated biometric tracking system used by coaches to track a variety of statistics about every player. The padded casing surrounds a unit that is commonly referred to as a GPS tracker, although it contains other measuring devices. The visible part is the packaging designed to protect both the electronics and the player from damage due to the usual impacts in rugby. The tracking system helps coaches keep tabs on various aspects of their players’ performance such as speed, distance covered, and tackles made. 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.