Unless you're shirtless, on a beach, playing something called "dogfight football" days before a secret, low-probability mission to destroy a nuclear reactor in some unidentified foreign state, there is only one ball.
It's particularly a basketball truism -- one that gets trotted out every time a team assembles a new collection of superstar players. But like with so many overused sports clichés, it's factually true and it also scratches at a theoretical truth about how the sport works. At any given moment in an offensive possession, only one player can be touching the ball. The other four players, then, must find ways to help their team score without the ball.
There are two very different things. The player with the ball needs to be able to physically manipulate it -- in order to get a shot off, to move it into a more valuable area on the court or pass to a teammate in a better position. They also need to know where all of their teammates are, anticipate where they're going and understand when to get rid of the ball. The players without the ball need to move quickly and use their bodies to create space for their teammates. They also need to know when to stop moving and statically occupy the valuable area they're already standing in. But for that last one to matter, they also do need to offer a credible threat of scoring if they do get the ball, otherwise the defense can just ignore them.
The best basketball teams are the ones that navigate this balance of responsibilities with the least friction. And the best basketball teams I've ever seen are the two title-winning Golden State Warriors sides from 2017 and 2018. Their rosters were filled with capable off-ball players, but also had two of the league's best on-ball players in Kevin Durant and Stephen Curry. The overlap in their abilities could have led to diminishing returns -- whenever one of them had the ball, the other player wasn't able to do what he did best -- but that didn't occur because they both also happened to be two of the best off-ball players in the league, thanks to their abilities to move and shoot.
Another sport where there's only one ball is soccer. So, why can't we look at it -- how players impact winning, how they fit together -- in the same way?