Wreckage the morning after fellow lost badly (7)
I believe the answer is:
flotsam
'wreckage' is the definition.
(flotsam is a kind of wreckage)
'the morning after fellow lost badly' is the wordplay.
'the morning' becomes 'am'.
'after' says to put letters next to each other.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'badly' is an anagram indicator.
'lost' is an anagram of 'lots'.
'f'+'lots'='flots'
'am' after 'flots' is 'FLOTSAM'.
(Other definitions for flotsam that I've seen before include "Goods lost" , "Wreckage found floating" , "Shipwreck goods floating" , "Vagrants" , "Wreck" .)