Resentful as the chap who's out of the race? (5)
I believe the answer is:
ratty
'resentful' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I don't see?
'the chap who's out of the race?' is the wordplay.
'the chap who' becomes 'ray' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'out of' means one lot of letters goes inside another (some letters on the outside of others).
'the race?' becomes 'tt'.
'ray' enclosing 'tt' is 'RATTY'.
'as' is the link.
Can you help me to learn more?
(Other definitions for ratty that I've seen before include "Mole's friend (The Wind in the Willows)" , "Short" , "Waspish" , "Cross - character in "The Wind in the Willows"" , "Characteristic of pest" .)