American uncle's performing as strong man (6)
I believe the answer is:
samson
'strong man' is the definition.
(I've seen this in another clue)
'american uncle's performing' is the wordplay.
'american uncle's' becomes 'Sam's' (Uncle Sam is a nickname for the USA).
'performing' becomes 'on' (as in being on stage).
'sams'+'on'='SAMSON'
'as' is the link.
(Other definitions for samson that I've seen before include "He loved Delilah" , "Strong man betrayed by Delilah" , "Strong Biblical hero" , "Delilah sheared him" , "Strong man brought down by Delilah" .)