American’s knockout has failed, punching morose drunk (9)
I believe the answer is:
smasheroo
'american's knockout' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'has failed punching morose drunk' is the wordplay.
'failed' is an anagram indicator.
'punching' is an insertion indicator (inserted letters punch or puncture others).
'drunk' indicates anagramming the letters.
'has' anagrammed gives 'ash'.
'morose' anagrammed gives 'smeroo'.
'ash' going within 'smeroo' is 'SMASHEROO'.
Can you help me to learn more?
(Other definitions for smasheroo that I've seen before include "hit" , "Stunner" , "thing of superlative quality" , "Top-rate person or thing (colloq.)" , "Very attractive person" .)