Men serving ball regularly caught by old stagers (6)

I believe the answer is:

valets

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'men' is the definition.
(I know this)

'ball regularly caught by old stagers' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'caught by' is an insertion indicator.
'old stagers' becomes 'vets' (I can't justify this - if you can you should believe this answer much more).
The alternate letters of 'ball' are 'al'.
'al' placed within 'vets' is 'VALETS'.

'serving' acts as a link.

Can you help me to learn more?

(Other definitions for valets that I've seen before include "Manservants" , "Gentlemen's gentlemen" .)

I've seen this clue in The Independent.

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