Crossword Genius

Searching on the ground floor as unlawful? (2,3,5)

Ross

I believe the answer is:

on all fours

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

'ground floor as unlawful?' is the definition.
I can't judge whether this definition defines the answer.

'searching on' is the wordplay.
I cannot really understand how this works, but
'on' is found in the answer.
The remaining letters 'allfours' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'the' is the link.

Can you help me to learn more?

(Other definitions for on all fours that I've seen before include "using arms and legs" , "in a defensive position" , "Maybe crawling" .)

I've seen this clue in The Guardian.
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