Uncontrollable excitement breaking out this year? (8)
I believe the answer is:
'uncontrollable excitement' is the definition.
(I've seen this before)
'breaking out this year?' is the wordplay.
'breaking out' is an anagram indicator.
'thisyear' is an anagram of 'HYSTERIA'.
(Other definitions for hysteria that I've seen before include "Problem of the uncontrolled" , "Uncontrolled emotion" , "Delirium - nervous disorder" , "display of wild emotion" , "Panic" .)