Start trouser pockets (5)
I believe the answer is:
rouse
'start' is the definition.
'trouser pockets' is the wordplay.
'pockets' indicates a hidden word (pocket can mean to contain).
'ROUSE' can be found hidden inside 'trouser'.
(Other definitions for rouse that I've seen before include "Prod" , "Move" , "Waken" , "Stir up; excite" , "Cause to become awake" .)