Vole fighting is the act of pitting at least two Cardassian voles against each other for entertainment purposes. Initiating or sponsoring such activity is considered a crime in Bajoran space, including Deep Space 9.
Quark often attempted to secretly stage vole fights in his bar. On one occasion in 2371 he, along with Morn, were caught by Odo painting numbers on the backs of several voles in preparation for a fight. Though Quark claimed that he was merely "counting them", he was arrested. (DS9: "Through the Looking Glass")
Later that same year, Quark again suggested vole fights would take place due to the presence of Cardassians on Deep Space 9, who were part of a joint Cardassian-Federation project to deploy a communications array in the Gamma Quadrant. He hoped that, in the future, more Cardassians would come to the station and initiate vole fights. Those hopes were quickly shot down by Odo and Benjamin Sisko who made it clear Quark would be held responsible for any vole fights on the Promenade, whether he initiated them or not. (DS9: "Destiny")