Where are you seeing "no athletic gear"?
The prohibited list only says:
- Potentially dangerous sporting equipment, including baseball and cricket bats, hockey and lacrosse sticks, pool cues, ski poles, fishing gear and archery equipment. (Golf clubs are permitted as long as they are stored inside your stateroom.)
I don't see anything else referring to athletic gear.
I will point out - I'm not sure they'll find a large enough area to throw a football around. There are lots of people on the beach, and no big empty areas for that sort of activity.