Keen on badminton, to some extent (4)

I believe the answer is:

into

'keen on' is the definition.
(if you're 'into' something you're keen on it)

'badminton to some extent' is the wordplay.
'to some extent' indicates a hidden word.
'INTO' is hidden within 'badminton'.

(Other definitions for into that I've seen before include "To a position within" , "Showing enthusiasm for" , "Taking an active and lively interest (in something)" , "Curious about" , "To a position inside" .)

I've seen this clue in The Times.

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