Musar על סנהדרין 91:6

Prior to the appointment of the first king, the Sanhedrin performed both functions, i.e. משפט התורה as well as הוראת שעה. This is one of the reasons Moses is referred to in our traditonal sources as מלך, king. This is also why, after the destruction of the Temple when Israel no longer had a king, Rabbi Eliezer is on record as saying: "I have heard that (nowadays) a Jewish Court of Law may administer corporal punishment even when Torah law does not call for this."