Crossword Genius

Surface damage caused by bad rust? (4)


I believe the answer is:


I'm a little stuck... Click here to teach me about this clue!

Here is my best explanation:

'surface damage caused' is the definition.
I can't tell whether this defines the answer.

'bad rust?' is the wordplay.
'bad' is an anagram indicator.
'rust' with letters rearranged gives 'RUTS'.

'by' is the link.

Can you help me to learn more?