Stars performing outside port (5)
I believe the answer is:
orion
'stars' is the definition.
(Orion is a constellation)
'performing outside port' is the wordplay.
'performing' becomes 'on' (as in being on stage).
'outside' indicates putting letters inside.
'port' becomes 'rio' (Rio de Janeiro is a port).
'on' enclosing 'rio' is 'ORION'.
(Other definitions for orion that I've seen before include "Major constellation" , "Mythical Greek hunter turned into constellation" , "Star" , "Prominent constellation" , "hero" .)