It could cause you to finish up with a nasty scar (5)
I believe the answer is:
scrap
'it could cause you' is the definition.
The definition suggests a singular noun which matches the answer.
'finish up with a nasty scar' is the wordplay.
'finish' means to take half the letters.
'with' means one lot of letters go next to another.
'a nasty' indicates an anagram (a nasty or wrong spelling).
'up' with half the letters taken is 'p'.
'scar' is an anagram of 'scra'.
'p' put after 'scra' is 'SCRAP'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for scrap that I've seen before include "Discard the small fragment" , "Fragment or remnant" , "Cancel; fight" , "Informal fight for waste material" , "Tussle over junk metal?" .)