Swimmer getting round me, admit disappointment (8)
I believe the answer is:
comedown
'disappointment' is the definition.
(comedown can mean a disappointment or anti-climax)
'swimmer getting round me admit' is the wordplay.
'swimmer' becomes 'cod' (type of fish).
'getting round' means one lot of letters goes inside another.
'admit' becomes 'own' (own can mean to admit or acknowledge).
'cod' going around 'me' is 'comed'.
'comed'+'own'='COMEDOWN'
(Other definitions for comedown that I've seen before include "Decrease" , "Do cowmen experience a loss of status?" , "Descent to a lower status" , "Decline in status" , "lessening of its effect?" .)