Light on one's feet
I believe the answer is:
spry
'light on one's feet' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for spry that I've seen before include "Sprightly" , "'Agile, nimble (4)'" , "Fleet" , "Quick and agile" , "'Active and lively, nimble (4)'" .)