Select a ball-point (3)
I believe the answer is:
opt
'select' is the definition.
(I've seen this before)
'a ball-point' is the wordplay.
'a ball' becomes 'o'.
'point' becomes 'pt' (**).
'o'+'pt'='OPT'
(Other definitions for opt that I've seen before include "Prefer, choose" , "Choose from pot" , "Elect" , "Decide between possibilities, choose" , "Pick from pot" .)