Squash book, not back-covers (5,2)

I believe the answer is:

tread on

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'squash' is the definition.
Although both the answer and definition are verbs in their base form, I don't understand how they can define each other.

'book not back-covers' is the wordplay.
'book' becomes 'read' (I've seen this before).
'back' says the letters should be written backwards.
'covers' indicates putting letters inside.
'not' in reverse letter order is 'ton'.
'read' going into 'ton' is 'TREAD ON'.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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