Make certain to reject right result (5)
I believe the answer is:
ensue
'result' is the definition.
('ensue' can be a synonym of 'result')
'make certain to reject right' is the wordplay.
'make certain' becomes 'ensure' ('ensure' can be a synonym of 'make certain').
'to reject' is a deletion indicator.
'right' becomes 'r' (common abbreviation).
'ensure' with 'r' taken out is 'ENSUE'.
(Other definitions for ensue that I've seen before include "Befall" , "Come about, result in" , "Follow afterwards" , "Occur as a result (of)" , "Come to pass" .)