Standard police department staff (9)
I believe the answer is:
yardstick
'standard' is the definition.
(I know that yardstick is a type of standard)
'police department staff' is the wordplay.
'police department' becomes 'yard' (Scotland Yard, HQ of the Metropolitan Police).
'staff' becomes 'stick' (I've seen this before).
'yard'+'stick'='YARDSTICK'
(Other definitions for yardstick that I've seen before include "Standard base for comparison" , "Standard of measurement" , "General measure for comparison" , "Criterion - means of measuring" , "Ruler or tape, three feet long" .)