Fight a big-headed beast (3)

I believe the answer is:

box

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

'fight' is the definition.
(boxing is a kind of fighting)

'a big-headed beast' is the wordplay.
'a big-headed' becomes 'b' (this could be a standard abbreviation which I don't know about).
'beast' becomes 'ox'.
'b'+'ox'='BOX'

Can you help me to learn more?

(Other definitions for box that I've seen before include "Carton" , "Spar; tree" , "Fight; tree; container" , "Receptacle" , "Wooden case" .)

I've seen this clue in the Evening Standard.

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