Potter’s letter read out (3)
I believe the answer is:
cue
'potter's' is the definition.
(a cue pots balls in snooker etc)
'letter read out' is the wordplay.
'letter' becomes 'q'.
'read out' indicates a 'sounds like' (homophone) clue.
'q' is a homophone of 'CUE'.
(Other definitions for cue that I've seen before include "Rod used in billiards" , "Signal for player" , "Prompting" , "Sports implement" , "A snooker ball striker" .)