I don't know if he was motivated to do this by a provision in his contract or just a general concern for his own health and safety, but one of the reports this morning said he had recently given up bike riding for safety reasons.
Not necessarily relevant specifically here, but pro athletes are often young men that are even less mature than their age cohort, and they have unbelievable amounts of money with which to indulge their thrill-seeking. Thus the vague ‘dangerous activities’ clauses. Possibly bike-riding, especially on public streets, is specifically prohibited. A player just might claim ‘fishing’ as a hobby when he buys a speedboat.