'Foul, ref!' Unai's getting worked up over nothing (9)
I believe the answer is:
nefarious
'foul' is the definition.
(thesaurus)
'ref unai's getting worked up over nothing' is the wordplay.
'getting' means one lot of letters go next to another.
'worked up' indicates an anagram.
'over' means one lot of letters goes inside another.
'nothing' becomes 'O' (looks like zero - 0).
'ref'+'unais'='refunais'
'refunais' anagrammed gives 'nefarius'.
'nefarius' placed around 'o' is 'NEFARIOUS'.
(Other definitions for nefarious that I've seen before include "immoral?" , "Villainous" , "Very bad" , "Wicked, criminal" , "Extremely wicked" .)