Enthusiastic about batting against spinner? No end (4)
I believe the answer is:
into
'enthusiastic about' is the definition.
(I've seen this before)
'batting against spinner? no end' is the wordplay.
'batting' becomes 'in'.
'against' says to put letters next to each other.
'spinner?' becomes 'top' (something that spins).
'no end' means to remove the last letter.
'top' with its final letter taken off is 'to'.
'in'+'to'='INTO'
(Other definitions for into that I've seen before include "Fascinated by" , "Curious about" , "Keen on, colloquially" , "Four this twelve is three" , "To a position within" .)