Up in arms, though one leg down? (7,3)
I believe the answer is:
hopping mad
'up in arms' is the definition.
(both can mean very angry)
'one leg down?' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'leg' could be 'pin' (pin is a kind of leg) and 'pin' is present in the answer.
'down?' could be 'd' and 'd' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'though' acts as a link.
(Other definitions for hopping mad that I've seen before include "Wild" , "Extremely angry (colloq.)" , "in angry mood" , "Furious (as a frog?)" , "like a kangaroo?" .)