On the ball, shimmying later (5)
I believe the answer is:
alert
'on the ball' is the definition.
(thesaurus)
'shimmying later' is the wordplay.
'shimmying' indicates anagramming the letters.
'later' with letters rearranged gives 'ALERT'.
(Other definitions for alert that I've seen before include "On the ball" , "Watchful; warning" , "Danger warning" , "Put on guard, warn" , "Watchfully awake" .)