They protect big races subject to disruption (8)

I believe the answer is:

ribcages

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

'they' is the definition.
Both the answer and definition are plural nouns.
Perhaps you can see an association between them that I don't see?

'protect big races subject to disruption' is the wordplay.
'big races' can be anagrammed to 'RIBCAGES'.
But, I am unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for ribcages that I've seen before include "They enclose chest-walls" , "Protective frameworks around body chests" .)

I've seen this clue in The Independent.

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.