Board Thread:Questions and Answers/@comment-38947763-20190921181204/@comment-38952966-20200524192429

We never see Ball Breaker summoned from Gyro, nor do we see anything indicating Gyro has any control over Ball Breaker after the steel ball is thrown. Ball Breaker always manifests from the steel ball, and only when the Super Spin is being used. No other Stand has this kind of limitation on being summoned except Tusk ACT 4, and that's just to use one aspect of Tusk rather than being integral to its use.

You can actually see during the Mandom fight that Gyro summons Scan briefly. It's definitely a Stand, not just an ability, and one that Gyro himself seems to summon. A third possibility for Ball Breaker's identity (that I forgot to mention in my original post) is that Ball Breaker is an upgraded form of Scan, powered up by the infinite rotation the same way Tusk ACT 4 is.

If a Stand can be used by more than one person, it's not really "their" Stand, is it? A Stand is a physical manifestation of a person's unique, distinct, energy, and Ball Breaker is not that. I don't buy that Hermit Purple is the Stand of all Hamon users, because that opens up a load more questions that don't make any sense. So the same is true here, if a Stand can be used by anyone who masters a certain energy (Hamon, the Spin, etc.), then it's the Stand of that energy and not really the individual. That's Occam's Razor kicking in.

That said, this whole mess is a lot more complicated than it should be because the rules of Stands changed a lot with Steel Ball Run and as a result we don't really have a lot of information, and Ball Breaker in particular is quite the silly sausage.