The Magen Avraham (308:45) explains, that the reason for the opinion that a ball is Muktzah on Shabbos, is because it is not considered a utensil that serves a necessary purpose.
Then he goes on to explain that it cannot even be used to cover a pot, because it is too dirty - which would seem to imply that if it’s clean, it wouldn’t be Muktzah
The question is: it says earlier (308:7) that the fact that something can be used for a different purpose (other than what it was made for) only helps if it comes from something which was once a utensil that was made for a necessary purpose - like a broken piece of furniture - so why does it seem from the Magen Avraham that it helps even for a ball - which like he himself said, does not serve a necessary purpose?