Showing initiative, gain admission using force (12)
I believe the answer is:
enterprising
'showing initiative' is the definition.
(I've seen this before)
'gain admission using force' is the wordplay.
'gain admission' becomes 'enter' (I've seen this before).
'using force' becomes 'prising' (as in prising something open).
'enter'+'prising'='ENTERPRISING'
(Other definitions for enterprising that I've seen before include "Adventurous and imaginative" , "Adventurous, resourceful" , "Venturesome" , "Showing initiative" , "daring" .)