Justify Edward returning first tennis shot (7)
I believe the answer is:
deserve
'justify' is the definition.
(I've seen this before)
'edward returning first tennis shot' is the wordplay.
'edward' becomes 'Ed' (short for Edward).
'returning' says the letters should be written backwards.
'first' says to put letters next to each other.
'tennis shot' becomes 'serve' (serve is a kind of tennis shot).
'ed' reversed gives 'de'.
'de'+'serve'='DESERVE'
(Other definitions for deserve that I've seen before include "Merit, earn" , "rate" , "Show one is worthy" , "Be entitled to" , "Severed (anag)" .)