What men threw overboard set out to clog nets (6)
I believe the answer is:
'what men threw overboard' is the definition.
(items jettisoned from a ship)
'set out to clog nets' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'to clog' becomes 'jam' (jam can mean to clog up).
'nets' indicates putting letters inside (some letters are contained or netted).
'set' anagrammed gives 'ets'.
'ets' put inside 'jam' is 'JETSAM'.
(Other definitions for jetsam that I've seen before include "it is scattered at sea" , "Goods thrown into the sea" , "Ship's discharge" , "Driftwood, wreckage" , "Items thrown overboard" .)