Small footwear: they might be hurting (9)

I believe the answer is:

strainers

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'be hurting' is the definition.
Although both the answer and 'hurting' are nouns, they are not in the same form of the noun.

'small footwear they' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'footwear' becomes 'trainer'.
'they' becomes 's' (I can't explain this - if you can you should believe this answer much more).
's'+'trainer'+'s'='STRAINERS'

'might' is the link.

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I've seen this clue in The Guardian.

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