No mater the inertial referential:
The pain is linked to the energy dissipated by the change of speed of the 2 objects in any inertial referential.

Remarque 1: a part of the energy can be absorbed by the ball by deformation or heating. So a soft ball would make less pain.

Remarque 2: The pain depends on what is static behind you and what is static behind the ball. Example in a squash court: you at 50km/h and ball at 50km/h will not produce the same pain further after the ball contact.