Better to go topless for one on casual walk (6)
I believe the answer is:
ambler
'one on casual walk' is the definition.
(to amble is to walk around casually)
'better to go topless' is the wordplay.
'better' becomes 'gambler' (a gambler is someone who bets).
'to go topless' means to remove the first letter.
'gambler' with its first letter removed is 'AMBLER'.
'for' is the link.
(Other definitions for ambler that I've seen before include "Eric -, English author (The Mask of Dimitrios)" , "Stroller" , "Writer called Eric" , "English thriller writer; walker" , "Fast-paced thriller writer? Yes" .)