Cricket side scoring boundaries only, apparently at a crawl (2,3,5)

I believe the answer is:

on all fours

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'apparently at a crawl' is the definition.
(crawling on all fours)

'cricket side scoring boundaries only' is the wordplay.
'cricket side' becomes 'on' (cricket term, on or leg side).
'scoring boundaries only' becomes 'allfours' (I can't explain this - if you can you should believe this answer much more).
'on'+'allfours'='ON ALL FOURS'

Can you help me to learn more?

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

I've seen this clue in The Telegraph.

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