Hacked off, having caught one, right behind seat (9)

I believe the answer is:

deckchair

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

'seat' is the definition.
(I know that deckchair is a type of seat)

I don't understand how the rest of the clue works.

(Other definitions for deckchair that I've seen before include "it's useful on Blackpool beach" , "support for holidaymaker" , "place to sit" .)

I've seen this clue in The Daily Express.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.