what is the block on the back of rugby shirts

The block on the back of rugby shirts is a GPS tracker. It is a sophisticated biometric tracking system used by coaches to track a variety of data, including players movements and performance during matches. The GPS tracker is a matchbox-sized capsule that is kept in place between the shoulder blades in something called a "Bro". The data provided by the GPS tracker can help both professional and amateur rugby players improve their performance. The GPS tracker is not a spare testicle, as suggested in one Reddit post.