Mount caught leg (5)
I believe the answer is:
climb
'mount' is the definition.
('climb' can be a synonym of 'mount')
'caught leg' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'leg' becomes 'limb' (I've seen this before).
'c'+'limb'='CLIMB'
(Other definitions for climb that I've seen before include "Go higher up" , "Use hands and feet to rise" , "Deadened" , "Rise to a higher level" , "Go up - scale" .)