Step-by-step explanation:
1) During the inhalation process when we breath in, our diaphragm contracts and moves downwards, This increases the space in our chest and accordingly our lungs expand. So, muscles between our ribs also get enlarged. As football player got fractured in the ribs and when ribs expands, he experiences pain during inhalation.
2) During the exhalation process, when we breath out, our diaphragm relaxes and moves upward. This decreases the space in our chest cavity and accordingly our lungs comes to normal. So, muscles between our ribs also relaxes. And that's why football player do not feel pain while exhaling.