Duck out of hole in loft, being fit (8)
I believe the answer is:
athletic
'being fit' is the definition.
(I've seen this before)
'duck out of hole in loft' is the wordplay.
'duck' becomes 'o'.
'out of' is a deletion indicator.
'in' means one lot of letters goes inside another.
'loft' becomes 'attic' ('attic' can be a synonym of 'loft'**).
'hole' with 'o' taken out is 'hle'.
'hle' put into 'attic' is 'ATHLETIC'.
(Other definitions for athletic that I've seen before include "Strong and active, good at sports" , "Good at running and jumping" , "Sporting, vigorous" , "Sporty, able-bodied" , "Given to partaking in sporting events" .)