Tasteless stuff supported by one French filmmaker (4)
I believe the answer is:
tati
'french filmmaker' is the definition.
(I've seen this in another clue)
'tasteless stuff supported by one' is the wordplay.
'tasteless stuff' becomes 'tat' (tat can mean worthless or tacky items).
'supported by' says to put letters next to each other (in a down clue, some letters hold up others).
'one' becomes 'i' (Roman numeral).
'tat'+'i'='TATI'
(Other definitions for tati that I've seen before include "Jacques -- (Monsieur Hulot's Holiday)" , "Jacques ----, French filmmaker" , "Jacques -, Fr. comedian" , "Jacques ___ , French comic actor and film director, d. 1982" , "Creator of Monsieur Hulot" .)