Straighten cast that's breaking into pieces (10)
I believe the answer is:
shattering
'breaking into pieces' is the definition.
'shattering' can be an answer for 'breaking' (shattering is a kind of breaking). I'm not sure about the 'into pieces' bit.
'straighten cast' is the wordplay.
'cast' indicates anagramming the letters (letters are dispersed or cast around).
'straighten' anagrammed gives 'SHATTERING'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for shattering that I've seen before include "Totally exhausting; breaking" , "being destructive" , "Very shocking" , "with devastating result" , "very upsetting" .)