Within reach, but ultimately you'll have to oust a big shot (6)
I believe the answer is:
double
'shot' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's an association between them I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for double that I've seen before include "With two equal parts" , "Twice - bent over - run" , "Second charge for the same offence" , "Increase twofold" , "Multiply by two" .)