Top criminal seizing power (7)
I believe the answer is:
spinner
'top' is the definition.
(as in a spinning top)
'criminal seizing power' is the wordplay.
'criminal' becomes 'sinner' (someone who has done bad deeds).
'seizing' means one lot of letters goes inside another.
'power' becomes 'p' (symbol in physics).
'sinner' placed around 'p' is 'SPINNER'.
(Other definitions for spinner that I've seen before include "Slow bowler - used to catch a mackerel?" , "Slow bowler - lure for mackerel" , "Type of bowler" , "One offering deliveries" , "revolutionary ball" .)