Stars performing across river (5)
I believe the answer is:
orion
'stars' is the definition.
(Orion is a constellation)
'performing across river' is the wordplay.
'performing' becomes 'on' (as in being on stage).
'across' means one lot of letters goes inside another.
'river' becomes 'rio' ('river' in Spanish).
'on' enclosing 'rio' is 'ORION'.
(Other definitions for orion that I've seen before include "Hunter slain by Artemis" , "Heavenly figure" , "A giant hunter in Greek legend, and a constellation" , "Great hunter of Greek myth, and a constellation" , "Mythical great hunter" .)