Guarantee to lose right result (5)
I believe the answer is:
ensue
'result' is the definition.
(to ensue is to occur or result)
'guarantee to lose right' is the wordplay.
'guarantee' becomes 'ensure' (synonyms).
'to lose' suggests deleting specific letters.
'right' becomes 'r' (common abbreviation).
'ensure' with 'r' removed is 'ENSUE'.
(Other definitions for ensue that I've seen before include "Happen or come about as consequence" , "Happen as a result, follow ( 5)" , "Proceed" , "Follow as a consequence" , "Turn out" .)