Her love was all for Leander (4)
I believe the answer is:
hero
'all for leander' is the definition.
The definition suggests a singular noun which matches the answer.
'her love' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'her'+'o'='HERO'
'was' acts as a link.
Can you help me to learn more?
(Other definitions for hero that I've seen before include "Man admired for courage and nobility" , "Conqueror" , "priestess of Aphrodite" , "Person distinguished by exceptional courage" , "Man of outstanding courage" .)