  The behaviour of sports balls during impact defines some special features of
each sport. The velocity of the game, the accuracy of passes or shots, the
control of the ball direction after impact, the risks of injury, are all set by
the impact mechanics of the ball. For inflated sports balls, those
characteristics are finely tuned by the ball inner pressure. As a consequence,
inflation pressures are regulated for sports played with inflated balls.
Despite a good understanding of ball elasticity, the source of energy
dissipation for inflated balls remains controversial. We first give a clear
view of non-dissipative impact mechanics. Second we review, analyse and
estimate the different sources of energy dissipation of the multi-physics
phenomena that occur during the impact. Finally, we propose several experiments
to decide between gas compression, shell visco-elastic dissipation, solid
friction, sound emission or shell vibrations as the major source of energy
dissipation.
