Corner section on the way up (4)
I believe the answer is:
trap
'corner' is the definition.
(I've seen this before)
'section on the way up' is the wordplay.
'section' becomes 'part' ('part' can be a synonym of 'section').
'on the way up' is a reversal indicator.
'part' reversed gives 'TRAP'.
(Other definitions for trap that I've seen before include "that can let an actor down" , "two-wheeler" , "Pitfall" , "Bunker; carriage" , "Snaring device" .)