Having the advantage, I grab over ten hat boxes (2,3,3,4)
I believe the answer is:
in the box seat
'having the advantage i grab over ten hat' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'boxes' is the wordplay.
I cannot really see how this works, but
an anagram of 'boxes' is 'eboxs' which is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for in the box seat that I've seen is " Has the advantage".)