Worker describing pit bully (8)
I believe the answer is:
domineer
'bully' is the definition.
(I know that domineer is a type of bully)
'worker describing pit' is the wordplay.
'worker' becomes 'doer' (doer is a kind of worker).
'describing' is an insertion indicator (describe can mean to form the outline of).
'pit' becomes 'mine' (mining pit).
'doer' enclosing 'mine' is 'DOMINEER'.
(Other definitions for domineer that I've seen before include "Deem iron to be changed to overbear" , "Ride roughshod over" , "Behave overbearingly" , "Exercise power over in an autocratic manner" , "Behave imperiously" .)