on the ball 1 : COMPETENT, KNOWLEDGEABLE, ALERT
<the other introductory essay... is much more on the ball -- Times
Literary Supplement> <keep on the ball> 2 : of ability or
competence <if the teacher has something on the ball,
the pupils won't squirm much -- New Yorker>
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=on+the+ball
According to Paul Dickson's New Dickson's Baseball Dictionary,
the phrase originated in the early 20th century U.S. in the sport of
baseball, where a pitcher who dominated and successfully
manipulated the opposing batters was said to "have" or
"be putting" a lot "on the ball," possibly referring to spin
or other sorts of sneaky pitcher tricks. From there the
phrase migrated into general use and acquired its
current sense of "able to handle whatever comes up."