Short trousers beginning to unsettle solicitor (4)
I believe the answer is:
tout
'solicitor' is the definition.
(someone who solicits business)
'short trousers beginning to unsettle' is the wordplay.
'short' becomes 'tot' (both can mean a small alcoholic drink).
'trousers' is an insertion indicator (to trouser can mean to steal or take).
'beginning to' indicates taking the first letters.
The initial letter of 'unsettle' is 'u'.
'tot' enclosing 'u' is 'TOUT'.
(Other definitions for tout that I've seen before include "Try to flog" , "Sell (tickets) illegally" , "Reseller of tickets at a profit" , "Attempt to sell (a thing)" , "Illegal ticket seller" .)