(use it in a sentence, leave it in a comment)
on the ball
quick to understand and to react to things, able to take action
(usually used with the verbs be, get and stay)
I didn’t sleep well last night and I’m not really on the ball today, I can’t concentrate on anything.
Although he’s 105 years old he’s definitely on the ball, he knows more about modern technology than people half his age do.
You need to get on the ball and start studying otherwise you’ll never pass the exam.
C’mon lazybones, don’t take a break now, stay on the ball, we have to have the house spick and span by the time the guests arrive!