American soldier's in trouble for slow movement (6)
I believe the answer is:
adagio
'slow movement' is the definition.
(I've seen this before)
'american soldier's in trouble' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'soldier' becomes 'gi' (government issue or general issue).
'in' indicates putting letters inside.
'trouble' becomes 'ado' (I've seen this before).
'a'+'gi'='agi'
'agi' inserted inside 'ado' is 'ADAGIO'.
'for' acts as a link.
(Other definitions for adagio that I've seen before include "In slow tempo" , "Slow movement (music)" , "Slow piece of music" , "' - - for Strings' (Barber)" , "Slow musical piece or movement" .)