Fit as Charlton? (8)
I believe the answer is:
athletic
'fit' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for athletic that I've seen before include "Sporty, able-bodied" , "Good at physical games" , "Good at running and jumping" , "Team" , "Fit and sporty" .)