Do men fight for seats in it? (3)

I believe the answer is:
box
'do' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for box that I've seen before include "Punch" , "Christmas present" , "Wooden case" , "Engage in pugilism" , "Present container?" .)
