In the past, you’d backed including place for second-in-command (6)

I believe the answer is:

deputy

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'for second-in-command' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for deputy that I've seen before include "mine safety official" , "Person acting on behalf of another" , "Assistant with power to act in the absence of superior" , "US sheriff's assistant" , "Member of the French parliament" .)

I've seen this clue in The Times.

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