Means to get hold of rudely fit swimmer (7)
I believe the answer is:
catfish
'swimmer' is the definition.
(catfish is a type of fish - fish swim)
'means to get hold of rudely fit' is the wordplay.
'means' becomes 'cash' (financial means).
'to get hold of' indicates putting letters inside.
'rudely' indicates anagramming the letters.
'fit' with letters rearranged gives 'tfi'.
'cash' enclosing 'tfi' is 'CATFISH'.
(Other definitions for catfish that I've seen before include "sea creature" , "Swimmer with whiskery barbels" , "It has whiskery barbells" , "Freshwater type" , "Bewhiskered swimmer?" .)