Chaps entering US team in disguise for fun (9)
I believe the answer is:
amusement
'fun' is the definition.
(thesaurus)
'chaps entering us team in disguise' is the wordplay.
'chaps' becomes 'men' (I've seen this before).
'entering' is an insertion indicator.
'in disguise' is an anagram indicator.
'us'+'team'='usteam'
'usteam' anagrammed gives 'amuset'.
'men' put within 'amuset' is 'AMUSEMENT'.
'for' acts as a link.
(Other definitions for amusement that I've seen before include "Pastime; recreation" , "set up through arcade?" , "enjoyment for 19 > [(type of) PARK]" , "(State of) finding something funny" , "Pleasant diversion by mute means (9)" .)