Support poles placed inside track (7)
I believe the answer is:
sponsor
'support' is the definition.
(I know that sponsor is a more specific form of the action support)
'poles placed inside track' is the wordplay.
'poles' becomes 'NS' (North and South poles).
'placed inside' indicates putting letters inside.
'track' becomes 'spoor' (track left by an animal).
'ns' inserted inside 'spoor' is 'SPONSOR'.
(Other definitions for sponsor that I've seen before include "Pledge money" , "Patron; promote" , "One financially supporting an activity" , "Supporter or champion" , "Provide backing" .)