Scandalous tirade is below standard (8)
I believe the answer is:
flagrant
'scandalous' is the definition.
(thesaurus)
'tirade is below standard' is the wordplay.
'tirade' becomes 'rant' (both can mean an angry outburst).
'is below' says to put letters next to each other (in a down clue, some letters go below others).
'standard' becomes 'flag' (standard is a type of flag).
'rant' after 'flag' is 'FLAGRANT'.
(Other definitions for flagrant that I've seen before include "Being shameless" , "Conspicuous, blatant" , "Blatant, outrageous" , "Patent" , "Barefaced" .)