Casting starting late is cause of irritation (7)
I believe the answer is:
itching
'irritation' is the definition.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for itching that I've seen before include "Having teasing desire" , "Yearning" , "It causes a desire to scratch" , "causing irritation?" , "causing pain" .)