be on the ball
slang To be attentive, knowledgeable, and quick to take action. I'm so glad that my assistant is always on the ball because I'm too scatterbrained to manage my schedule on my own. I can't believe Molly got that report done so quickly—she's really on the ball.
on the ball, be
Also, have something on the ball. Be especially capable or efficient, as in These programmers really have a lot on the ball. This term originated in baseball, where it was used for throwing a pitch with exceptional speed, spin, or some other deceptive motion. [Slang; early 1900s]