what is the rectangle on the back of rugby shirts

The rectangle on the back of rugby shirts is a GPS tracking device. This device is part of a sophisticated biometric tracking system used by coaches to track a variety of data, such as the distance covered, speed, and heart rate of players during training and matches. The device is usually located on the upper back of the shirt, between the shoulders. The data collected by the GPS tracking device can help coaches and players analyze performance and make improvements to training and game strategies.