Rich team surprisingly losing one second fixture (7)
I believe the answer is:
rematch
'rich team surprisingly losing one' is the definition.
I can't judge whether this defines the answer.
'second fixture' is the wordplay.
'second' becomes 're' (prefix meaning second in eg review, re-education).
'fixture' becomes 'match' (sporting fixture).
're'+'match'='REMATCH'
Can you help me to learn more?
(Other definitions for rematch that I've seen before include "Another game" , "Further engagement of the same contestants" , "Return fixture" , "Teams' second game" , "Return game" .)