One fellow helping another at an American match (9)

I believe the answer is:

groomsman

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

'helping another at an american match' is the definition.
I can't tell whether this definition defines the answer.

'one fellow' is the wordplay.
'one' becomes 'grooms' (I can't justify this - if you can you should give a lot more credence to this answer).
'fellow' becomes 'man' (fellow can mean a man).
'grooms'+'man'='GROOMSMAN'

Can you help me to learn more?

(Another definition for groomsman that I've seen is " Male wedding attendant".)

I've seen this clue in The Telegraph.

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