In court a substitute for nothing (4)
I believe the answer is:
love
'nothing' is the definition.
(love means zero in tennis)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for love that I've seen before include "like very much?" , "powerful emotion" , "Nothing for the Williams sisters?" , "No score, sweetheart" , "See 10" .)