While I’m sorry he was injured, he can’t blame everything on the gym or the ball. Whatever happened to taking responsibility for one’s own actions?
Maybe he has a legitimate complaint. If the fellow was using the ball in a manner prescribed by the YMCA, and if the ball failed due to some manufacturing defect, then I don't see how you can blame the guy who got hurt.
If, OTOH, the use was non-standard and the ball was OK, then he's got no case.
There is more to this story than reported (as is often the case). He was apparently working out under the supervision of a YMCA personal trainer...