Stretch no clothing when you do this run (6)
I believe the answer is:
I believe this is a double definition.
'stretch' is the first definition.
'no clothing when you do this run' is the second definition.
(a streak is a naked run)
(Other definitions for streak that I've seen before include "'Sudden flash, of lightning say (6)'" , "Move very fast; thin strip" , "Irregular contrasting stripe" , "Unbroken series, of luck say" , "Run naked as stunt" .)