Commit urban offence: spit on recreation ground (6-4)

I believe the answer is:

double-park

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'commit' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how one could define the other.

'urban offence spit on recreation ground' is the wordplay.
'urban offence spit' becomes 'double' (I can't explain this - if you can you should believe this answer much more).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'recreation ground' becomes 'park' (I've seen this before).
'double'+'park'='DOUBLE-PARK'

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I've seen this clue in The Independent.

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