Love delving into favourite writer (4)
I believe the answer is:
poet
'writer' is the definition.
(poet is a kind of writer)
'love delving into favourite' is the wordplay.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'delving into' means one lot of letters goes inside another.
'favourite' becomes 'pet' ('pet' can be a synonym of 'favourite').
'o' going within 'pet' is 'POET'.
(Other definitions for poet that I've seen before include "'Paul Muldoon or Paula Meehan, say (4)'" , "Burns was one" , "Burns, for example" , "Masefield, for instance" , "Tope with a versifier" .)