Disbelief upset his team (7)
I believe the answer is:
atheism
'disbelief' is the definition.
(I've seen this before)
'upset his team' is the wordplay.
'upset' indicates an anagram.
'his'+'team'='histeam'
'histeam' with letters rearranged gives 'ATHEISM'.
(Other definitions for atheism that I've seen before include "Owed" , "displaying opposition to religion" , "Disbelief in gods" , "Non-belief in God" , "Sceptic's position" .)