Detectives arresting a large number about driving (7)
I believe the answer is:
dynamic
'driving' is the definition.
(similar in meaning)
'detectives arresting a large number about' is the wordplay.
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'arresting' is an insertion indicator.
'a large number' becomes 'many' (many means lots of something).
'about' says the letters should be written backwards.
'cid' going around 'many' is 'cimanyd'.
'cimanyd' written backwards gives 'DYNAMIC'.
(Other definitions for dynamic that I've seen before include "High-powered" , "I'm Candy (anag) - full of beans" , "Vigorous and effective" , "Driving" , "Powerful and vigorous" .)