Rules of Snooker:
3. Mode of Play
(c) The first player plays from in-hand, the frame commencing when the cueball has been placed on the table and contacted by the tip of the cue either:
(i) as a stroke is made; or
(ii) while addressing the cue-ball.
5. Playing from In-hand
(b) If the tip of the cue should touch the cue-ball while positioning it, and the referee is satisfied that the striker was not attempting to play a stroke, then the cue-ball is not in play.
https://www.wpbsa.com/governance/rules-of-snooker/