Struggle with inability to relax? Not half (7)
I believe the answer is:
wrestle
'struggle' is the definition.
(I know that wrestle is a type of struggle)
'with inability to relax? not half' is the wordplay.
'with' becomes 'w' (abbreviation).
'inability to relax?' becomes 'restlessness'.
'not half' indicates taking half.
'restlessness' with half the letters taken is 'restle'.
'w'+'restle'='WRESTLE'
(Other definitions for wrestle that I've seen before include "Fight - get to grips (with)" , "Tussle" , "Grapple; strive" , "Fight; struggle" , "Struggle physically or mentally" .)