Must aid rebuilding of the arena (7)
I believe the answer is:
stadium
'the arena' is the definition.
('stadium' can be a synonym of 'arena')
'must aid rebuilding' is the wordplay.
'rebuilding' indicates anagramming the letters.
'must'+'aid'='mustaid'
'mustaid' is an anagram of 'STADIUM'.
'of' is the link.
(Other definitions for stadium that I've seen before include "Admit us (anag) - sports ground" , "A major sports ground" , "eg Yankee, Wembley" , "Venue for sporting events, concerts etc" , "Sports arena" .)