Jumps on one foot (4)
I believe the answer is:
hops
'jumps on one foot' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hops that I've seen before include "Leaps on one leg" , "Shop around for beer material" , "(Little) jumps" , "Dances -- beer ingredient" , "what could make you bitter" .)