Some congratulate trampolinist or swimmer (5)
I believe the answer is:
tetra
'swimmer' is the definition.
(tetra is a kind of fish)
'some congratulate trampolinist or' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'TETRA' can be found hidden inside 'congratulate trampolinist or'.
(Other definitions for tetra that I've seen before include "Small tropical fish" , "With four parts" , "Accosting and detaining (someone)" , "Bright fish; four (prefix)" , "starter for four" .)