It is far too common amongst athletes to be stiff between their neck and the bottom of their ribcage (the thoracic spine or T-spine.) Most often, lack of mobility in this region is expressed by a resultant lack of shoulder flexion (raising your arms up over your head.) In most daily activites, poor t-spine mobility is hardly a limiting factor, but... In positions requiring overhead support like a press or overhead squat, positions of dynamic shoulder loading like the kipping pull up, and in positions of static strength like the front squat, it becomes painfully clear that lack of mobility of the T-spine leads to overall decreases in applications of strength and power throughout the kinetic chain. That is your overhead squat, the speed of your tennis serve, or the amount of glide you get during each swim stroke is likely a function of your t-spine mobility. The good news is, that mobilising this region of the spine is relatively easy and will lead to immediate, meaningful changes in functional status. So, ask your coach about how you can do something about your stiff rib cage.
Excellent Thoracic Extension is one reason K Graves is so strong overhead.