Criminal once more losing nothing -- he often argued with the court's judges (7)
I believe the answer is:
'he often argued with the court's judges' is the definition.
(John McEnroe argued with tennis umpires a lot)
'criminal once more losing nothing' is the wordplay.
'criminal' is an anagram indicator.
'losing' indicates named letters should be taken away.
'nothing' becomes 'O' (O resembles 0).
'oncemore' with 'o' removed is 'ncemore'.
'ncemore' is an anagram of 'MCENROE'.
(Other definitions for mcenroe that I've seen before include "John --, US tennis player" , "he's noted for being controversial" , "Tennis star" .)