Travelling to open air performance (9)
I believe the answer is:
operation
'performance' is the definition.
(I've seen this before)
'travelling to open air' is the wordplay.
'travelling' is an anagram indicator.
'to'+'open'+'air'='toopenair'
'toopenair' anagrammed gives 'OPERATION'.
(Other definitions for operation that I've seen before include "financial transaction" , "To one pair (anag.)" , "Handling" , "Act of surgery" , "military undertaking" .)