Climbing aid in hamper by leg (7)
I believe the answer is:
crampon
'climbing aid' is the definition.
(I've seen this before)
'hamper by leg' is the wordplay.
'hamper' becomes 'cramp' (both can mean to frustrate or hinder).
'by' says to put letters next to each other.
'leg' becomes 'on' (cricket term, fielding positions).
'cramp'+'on'='CRAMPON'
'in' is the link.
(Other definitions for crampon that I've seen before include "Spike attached to the shoe to prevent slipping when climbing" , "Grappling-iron" , "Climber's device" , "Gripping device" , "Climbing accessory" .)