It attacks the horse (7)

I believe the answer is:

charger

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'horse' is the definition.
(I know that charger is a type of warhorse)

I can't explain the rest of the clue.

(Other definitions for charger that I've seen before include "I expect payment" , "old dish" , "One loading" , "A warhorse; a serving-dish" , "needed for battery" .)

I've seen this clue in the Evening Standard.

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