Police beginning to excavate wooded area (5)
I believe the answer is:
copse
'wooded area' is the definition.
(I've seen this in another clue)
'police beginning to excavate' is the wordplay.
'police' becomes 'cops' (cop can informally mean a police officer).
'beginning to' indicates taking the first letters.
The initial letter of 'excavate' is 'e'.
'cops'+'e'='COPSE'
(Other definitions for copse that I've seen before include "Small thicket" , "Scope for a small wood" , "Dense growth of bushes or trees" , "Stand of trees" , "Piece of managed woodland" .)