Right inside stop the wrinkle (6)
I believe the answer is:
crease
'the wrinkle' is the definition.
('crease' can be a synonym of 'wrinkle')
'right inside stop' is the wordplay.
'right' becomes 'R' (common abbreviation).
'inside' is an insertion indicator.
'stop' becomes 'cease' (synonyms).
'r' inserted into 'cease' is 'CREASE'.
(Other definitions for crease that I've seen before include "Where the batsman stands" , "ruck" , "Fold - wrinkle" , "Fold in clothing" , "Line caused by folding or pressing, cloth or paper" .)