Rodent performing in shop (3,2)
I believe the answer is:
rat on
'shop' is the definition.
(both can mean to betray or inform upon)
'rodent performing' is the wordplay.
'rodent' becomes 'rat' (rat is a kind of rodent).
'performing' becomes 'on' (as in being on stage).
'rat'+'on'='RAT ON'
'in' acts as a link.
(Other definitions for rat on that I've seen before include "Betray" , "shop" , "Give away" , "desert" , "grass up" .)