Crossword Genius

Famous runner one encountered on stairs? (9)

Ross

I believe the answer is:

bannister

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

'famous runner' is the definition.
(I've seen this before)

'one encountered on stairs?' is the wordplay.
I cannot quite see how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for bannister that I've seen before include "Famous runner" , "safety feature for flight" , "Sir Roger --, first sub-four-minute miler" , "Roger --, four-minute miler" , "security feature" .)

I've seen this clue in The Times.
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