Promising individual shot unarmed cop (2-3-5)

I believe the answer is:

up-and-comer

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

'shot unarmed cop' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'promising individual' is the wordplay.
I cannot quite understand how this works, but
'individual' could be 'comer' (comer is a kind of individual) and 'comer' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

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