Penrith's foremost supporter comes back drunk, a little cooked (9)
I believe the answer is:
parboiled
'cooked' is the definition.
(parboiling is a kind of cooking)
'penrith's foremost supporter comes back drunk' is the wordplay.
'foremost' indicates taking the first letters.
'supporter' becomes 'bra' (a bra gives support to breasts).
'comes back' says the letters should be written in reverse.
'drunk' becomes 'oiled' (I've seen this before).
The first letter of 'penriths' is 'p'.
'bra' reversed gives 'arb'.
'p'+'arb'+'oiled'='PARBOILED'
'a little' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Another definition for parboiled that I've seen is " Broad pile (anag.)".)