Large number nabbed by detectives. returning with powerful force (7)
I believe the answer is:
dynamic
'with powerful force' is the definition.
(dynamic means great force or power)
'large number nabbed by detectives returning' is the wordplay.
'large number' becomes 'many' (many means lots of something).
'nabbed by' means one lot of letters goes inside another (nab can mean to steal or take possession of).
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'returning' is a reversal indicator.
'many' put within 'cid' is 'cimanyd'.
'cimanyd' in reverse letter order is 'DYNAMIC'.
(Other definitions for dynamic that I've seen before include "Having power" , "Driving" , "Constantly changing" , "Very active" , "High-powered" .)