How you chuck it away when the injured arm has mended? (5)

I believe the answer is:

sling

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

'it away when the injured arm has mended?' is the definition.
The definition suggests a singular noun which matches the answer.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for sling that I've seen before include "shy" , "Old weapon or supporting strap" , "Move off!" , "Catapult or support as for injured arm" , "throwing implement like catapult" .)

I've seen this clue in the Evening Standard.

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.