How angry was the wallaby? (7,3)

I believe the answer is:

hopping mad

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

'how angry' is the definition.
'hopping mad' can be an answer for 'angry' (hopping mad means very angry). I am not sure about the 'how' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for hopping mad that I've seen before include "In a terrible rage" , "in high dudgeon" , "Very irate" , "in angry mood" , "Extremely angry (colloq.)" .)

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

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