They watch attractive people running (7-2)

I believe the answer is:

lookers-on

'they watch' is the definition.

'attractive people running' is the wordplay.
'attractive people' becomes 'lookers' (I've seen this before).
'running' becomes 'on' (I've seen this in other clues).
'lookers'+'on'='LOOKERS-ON'

(Another definition for lookers-on that I've seen is " Witnesses".)

I've seen this clue in The Independent.

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