Prop used by non-leading actors (7)
I believe the answer is:
'prop' is the definition.
(I know that prop is a more specific form of the action support)
'non-leading actors' is the wordplay.
I cannot quite see how this works, but
'leading' could be 'up' (up can mean leading in a game) and 'up' is found in the answer.
The remaining letters 'sport' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'used by' is the link.
Can you help me to learn more?
(Other definitions for support that I've seen before include "Hold up" , "Maintain, back" , "Provide with food, clothing and shelter, or encouragement" , "Uphold" , "second" .)