A group of detectives in charge is sharp (6)
I believe the answer is:
acidic
'sharp' is the definition.
(thesaurus)
'a group of detectives in charge' is the wordplay.
'group of detectives' becomes 'cid' (Criminal Investigation Department).
'in charge' becomes 'ic'.
'a'+'cid'+'ic'='ACIDIC'
'is' acts as a link.
(Other definitions for acidic that I've seen before include "Unpleasant" , "Sharp-tasting, sour" , "scathing?" , "Sarcastic or sour" , "Like vinegar" .)