To be “on the ball” means to be at the top of your game.
We have all heard a pitcher’s excuse of not having his “stuff” after a bad outing and wondered how that excuse would work with our bosses if we had a bad day.
From the early days of baseball, when a pitcher couldn’t find the spin and lost control, it’s been said he had “nothing on the ball” which gave us “on the ball” as meaning “he’s in control.”
We often say that someone who is sharp is “on the ball”.
Ok, but what does it mean when you say “at the top of your game”?
On the ball came from connecting a trailer to a vehicle. When one is backing up to the trailer, the receiver will be over the ball. Now, “You’re on the ball” meaning, you’re in proper position or correct!