Train a German runner? (7)

I believe the answer is:

manager

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

'runner?' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'train a german' is the wordplay.
'a german' anagrams to 'MANAGER'.
Though, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for manager that I've seen before include "Coach" , "suit?" , "One in charge of staff" , "Director" , "Boss" .)

I've seen this clue in The Daily Mail.

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