Waiting nervously for outcome, swimming not the snooker (2,11)
I believe the answer is:
on tenterhooks
'waiting nervously for outcome' is the definition.
(on tenterhooks means waiting for something)
'swimming not the snooker' is the wordplay.
'swimming' indicates an anagram.
'not'+'the'+'snooker'='notthesnooker'
'notthesnooker' anagrammed gives 'ON TENTERHOOKS'.
(Other definitions for on tenterhooks that I've seen before include "In suspense - or so to Kenneth (anag)" , "In a state of suspense" , "In impatient suspense" , "In agitated suspense" , "Keyed up in anticipation" .)