A proportion of leaf carrying recent damage (10)
I believe the answer is:
'a proportion' is the definition.
(I know that percentage is a type of proportion)
'leaf carrying recent damage' is the wordplay.
'leaf' becomes 'page' (page is a kind of leaf).
'carrying' means one lot of letters goes inside another.
'damage' indicates anagramming the letters (I've seen 'damaged' mean this).
'recent' anagrammed gives 'ercent'.
'page' enclosing 'ercent' is 'PERCENTAGE'.
'of' is the link.
(Other definitions for percentage that I've seen before include "Proportion, share" , "Proportion stated in hundredth parts" , "Proportion in each 100" , "cut?" , "Maybe commission" .)