Clashing with stand-in — so unfortunately (9)
I believe the answer is:
dissonant
'clashing' is the definition.
(thesaurus)
'stand-in so unfortunately' is the wordplay.
'unfortunately' indicates anagramming the letters (a bad or unfortunate spelling).
'stand'+'in'+'so'='standinso'
'standinso' is an anagram of 'DISSONANT'.
'with' acts as a link.
(Other definitions for dissonant that I've seen before include "incongruous" , "Lacking harmony" , "grating" , "sounding harsh" .)