Saddle strap, right when adjusted (5)
I believe the answer is:
girth
'saddle strap' is the definition.
(strap on a horse's saddle)
'right when adjusted' is the wordplay.
'when adjusted' indicates an anagram.
'right' is an anagram of 'GIRTH'.
(Other definitions for girth that I've seen before include "Distance around, often of the tummy" , "Distance round a body" , "Band around a horse's belly" , "Measurement around the waist" , "The distance around a thing or tummy" .)