Trunks almost all removed — smashing result for swimmers (7)
I believe the answer is:
turtles
'swimmers' is the definition.
(turtles swim)
'trunks almost all removed smashing result' is the wordplay.
'almost all removed' indicates taking the first letters (all but the first letter removed).
'smashing' indicates anagramming the letters.
The first letter of 'trunks' is 't'.
'result' is an anagram of 'urtles'.
't'+'urtles'='TURTLES'
'for' is the link.
(Other definitions for turtles that I've seen before include "Marine reptiles" , "Let rust settle on sea-creatures" , "The reptiles are let rust" , "Swimming reptiles" , "Reptiles with bony shell and flipper-like limbs" .)