Leg's midpoint (4)
I believe the answer is:
knee
'leg's midpoint' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for knee that I've seen before include "Hinge between the thigh and the shin" , "Joint protected by the patella" , "One has a cap" , "may present problem to maid" , "joint input" .)