Stones in a mix-up cause excitement (9)
I believe the answer is:
sensation
'cause excitement' is the definition.
'sensation' can be an answer for 'excitement' (sensation is a kind of excitement). I am unsure of the 'cause' bit.
'stones in a mix-up' is the wordplay.
'mix-up' indicates an anagram.
'stones'+'in'+'a'='stonesina'
'stonesina' anagrammed gives 'SENSATION'.
Can you help me to learn more?
(Other definitions for sensation that I've seen before include "Scandal" , "Scandalous news item" , "Feeling; thrilling person or thing" , "Feeling produced by stimulation, or dramatic news (9)" , "Physical feeling or perception" .)