Toss rowers around shallow end — they aren't heavy (13)
I believe the answer is:
welterweights
'they aren't heavy' is the definition.
(a welterweight is a relatively light boxer)
'toss rowers around shallow end' is the wordplay.
'toss' becomes 'welter' (welter can mean to move or writhe).
'rowers' becomes 'eights' (eight can mean a crew of eight rowers).
'around' is an insertion indicator.
'end' suggests the final letters.
The final letter of 'shallow' is 'w'.
'welter'+'eights'='weltereights'
'weltereights' placed around 'w' is 'WELTERWEIGHTS'.
I've seen this clue in The Guardian.
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