adverb (or adjective)
1. slang : knowledgeable and competent : purposively active : alert
she was no chicken perhaps, but she was on the ball — Theodora Keogh
when the men know some of the lesson, the instructor really has to stay on the ball — Infantry Journal
2. slang : of ability : of competence
to have a lot on the ball
the average man of 40 had appreciably more on the bll than the person of 30 — J.E.Gibson