To boot into goal, softly (4)
I believe the answer is:
also
'to boot' is the definition.
(I've seen this before)
'into goal softly' is the wordplay.
'into' indicates a hidden word.
'ALSO' is hidden within 'goal softly'.
(Other definitions for also that I've seen before include "on top" , "Furthermore" , "Plus" , "Additionally" , "admitted to Royal Society > too" .)