Be wrong about hard climb (4)
I believe the answer is:
shin
'climb' is the definition.
(shinning is a kind of climbing)
'be wrong about hard' is the wordplay.
'be wrong' becomes 'sin' (I've seen this before**).
'about' is an insertion indicator.
'hard' becomes 'h'.
'sin' going around 'h' is 'SHIN'.
(Other definitions for shin that I've seen before include "letter from Israel" , "Part of the lower leg" , "Body part" , "Long bone between knee and ankle" , "Leg-bone" .)