Clue: What'll damage seat, with cutting in? (5)
Answer: TAWSE
Explanation: Definition: What'll damage seat, with cutting in
*(seat) with **W**(ith) *cutting in* and &lit. 
A tawse, as I can testify from personal experience, was a leather belt used by teachers to punish schoolchildren in Scotland when corporal punishment was still allowed, although I don't remember my seat being whacked – it was always my hand as far as I can remember.