Aggressor and detective court witness? (4-3)

I believe the answer is:

hawk-eye

'court witness?' is the definition.
(computer system used on a tennis court)

'aggressor and detective' is the wordplay.
'aggressor' becomes 'hawk' (advocate of war, as opposed to a dove).
'and' says to put letters next to each other.
'detective' becomes 'eye' (as in a private eye).
'hawk'+'eye'='HAWK-EYE'

I've seen this clue in The Guardian.

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