No stand-downs on a kind of exercise (3-3)
I believe the answer is:
sit-ups
'no stand-downs' is the definition.
I know nothing about this answer so I can't tell whether this works.
'on a kind of exercise' is the wordplay.
'on' is a charade indicator (letters next to each other).
'a kind of' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'exercise' becomes 'situp' (I've seen this before).
's' put after 'situp' is 'SIT-UPS'.
Can you help me to learn more?
(Other definitions for sit-ups that I've seen before include "Physical training exercises" , "Gym exercises" , "Tummy tighteners" .)