Mark, caught by rebounding bullets, say (5)
I believe the answer is:
comma
'mark' is the definition.
(punctuation mark)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for comma that I've seen before include "shortest interval" , ", (stet)" , "I signal a break" , "Punctuation mark - butterfly" , "Kind of butterfly" .)