Spectator's wife is sent off (7)
I believe the answer is:
witness
'spectator's' is the definition.
('witness' can be a synonym of 'spectator')
'wife is sent off' is the wordplay.
'wife' becomes 'w' (**).
'off' indicates anagramming the letters.
'is'+'sent'='issent'
'issent' is an anagram of 'itness'.
'w'+'itness'='WITNESS'
(Other definitions for witness that I've seen before include "Evidence, proof" , "Court testifier" , "One giving evidence" , "See (an event or crime)" , "Spectator" .)