Shame leader of American party (5)
I believe the answer is:
abash
'shame' is the definition.
(I've seen this before)
'leader of american party' is the wordplay.
'leader of' says to take the initial letters.
'party' becomes 'bash' (term for a party or celebration).
The first letter of 'american' is 'a'.
'a'+'bash'='ABASH'
(Other definitions for abash that I've seen before include "Disconcert" , "Cause someone to feel embarrassed" , "Bring shame on" , "Cause to feel ashamed" , "show up" .)