Starts pulling away, cautiously yet quick (4)
I believe the answer is:
pacy
'quick' is the definition.
'starts pulling away cautiously yet' is the wordplay.
'starts' indicates taking the first letters.
The first letters of 'pulling away cautiously yet' is 'PACY'.
(Other definitions for pacy that I've seen before include "Showing good turn of speed" , "Fast" , "Fleet" , "nippy" .)