on the ball, be - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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]