Drop stock complaint during trouble (6)
I believe the answer is:
abseil
'drop' is the definition.
(abseiling is dropping down a surface)
'stock complaint during trouble' is the wordplay.
'stock complaint' becomes 'BSE' (mad cow disease or BSE affects cattle or stock).
'during' means one lot of letters goes inside another.
'trouble' becomes 'ail' (synonyms).
'bse' going into 'ail' is 'ABSEIL'.
(Other definitions for abseil that I've seen before include "Descend rock-face using a doubled rope - like Isabel" , "Descend vertical slope using rope" , "Descend vertically by rope" , "Climb down using a double rope" , "Is able (anag.)" .)