New dawn since arenas rebuilt (11)
I believe the answer is:
renaissance
'new dawn' is the definition.
(both can mean a new beginning or rebirth)
'since arenas rebuilt' is the wordplay.
'rebuilt' indicates an anagram.
'since'+'arenas'='sincearenas'
'sincearenas' anagrammed gives 'RENAISSANCE'.
(Other definitions for renaissance that I've seen before include "New birth" , "Rebirth" , "Time with hint of modernity" , "Awakening" , "revival starting in Florence" .)