It rusted badly, turning into debris (8)
I believe the answer is:
detritus
'debris' is the definition.
(I know that debris can be written as detritus)
'it rusted badly' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'it'+'rusted'='itrusted'
'itrusted' anagrammed gives 'DETRITUS'.
'turning into' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for detritus that I've seen before include "Loose material worn away from rocks" , "Bits and pieces of rubbish" , "Loose eroded matter" , "Rubbish - it rusted (anag)" , "Accumulation of debris - it rusted (anag)" .)