They'll leap at a chance to fight (12)

I believe the answer is:

paratroopers

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

'chance to fight' is the definition.
I can't tell whether this defines the answer.

'they'll leap at a' is the wordplay.
I cannot quite understand how this works, but
'at' is present in the answer.
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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