Rant at rotten Scots material (6)
I believe the answer is:
tartan
'scots material' is the definition.
(I've seen this before)
'rant at rotten' is the wordplay.
'rotten' is an anagram indicator.
'rant'+'at'='rantat'
'rantat' anagrammed gives 'TARTAN'.
(Other definitions for tartan that I've seen before include "dress?" , "Distinctive cloth pattern of a Highlands clan" , "Scottish plaid design" , "Scottish woollen cloth" , "Cloth with a crisscross design" .)