Which racehorses run after spires? (14)

I believe the answer is:

steeplechasers

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'which racehorses' is the definition.
I can't tell whether this definition defines the answer.

'run after spires?' is the wordplay.
'run' becomes 'steeplechase' (steeplechase is a kind of run).
'after spires?' becomes 'rs' (I can't justify this - if you can you should believe this answer much more).
'steeplechase'+'rs'='STEEPLECHASERS'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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