He's defeated Ivor, perhaps, out of court (6)
I believe the answer is:
victor
'he's defeated' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'ivor perhaps out of court' is the wordplay.
'perhaps' indicates anagramming the letters.
'out of' means one lot of letters goes inside another.
'court' becomes 'ct' (abbreviation used in road names).
'ivor' is an anagram of 'vior'.
'vior' going around 'ct' is 'VICTOR'.
Can you help me to learn more?
(Other definitions for victor that I've seen before include "Winning contestant" , "The one who wins the battle" , "Oh dear!" , "''To the . . . . . . the spoils'' (6)" , "Meat; complain" .)