Swimming fish caught by crew (7)
I believe the answer is:
reeling
'swimming' is the definition.
(I've seen this before)
'fish caught by crew' is the wordplay.
'fish' becomes 'eel' (eel is a type of fish).
'caught by' indicates putting letters inside.
'crew' becomes 'ring' (both can mean a group of people).
'eel' inserted inside 'ring' is 'REELING'.
(Other definitions for reeling that I've seen before include "Staggering about in Irish dance?" , "Unable properly to control one's movements" , "Swimming" , "Punchy" , "Dancing; staggering" .)