He fights with oarsmen on boat (13)

I believe the answer is:

cruiserweight

I'm a little stuck... Click here to teach me more about this clue!

'he fights with oarsmen on boat' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

'he fights with oarsmen on' is the wordplay.
'he fights' becomes 'cruiser' (I can't justify this - if you can you should give a lot more credence to this answer).
'with' becomes 'w' (abbreviation).
'oarsmen' becomes 'eight' (I've seen this before).
'on' says to put letters next to each other.
'cruiser'+'w'+'eight'='CRUISERWEIGHT'

Can you help me to learn more?

(Another definition for cruiserweight that I've seen is " Boxing class".)

I've seen this clue in The Independent.

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