Order unanimously reversed, without costs and motion for stay of arbitration granted pending trial, and matter remitted for trial of the issue of the existence of a "hit and run" vehicle. Memorandum: When insured persons duly demand arbitration of their claims the insurer can obtain a stay of the demand only upon tendering an issue which the court must determine prior to arbitration. Although such an issue cannot be presented by mere conclusory allegations by the insurer ( Matter of Fuscaldo [ MVAIC], 24 A.D.2d 744), the allegations in support of petitioner-appellant's motion to stay arbitration in this case are factual, denying the existence of a "hit and run" vehicle in the accident in which the insureds were injured, and they are not insufficient as conclusory. Respondents, as insured persons, have the burden to prove that the accident was caused by a "hit and run" vehicle ( McCarthy v. MVAIC, 16 A.D.2d 35, 39), and so this matter must be remitted for trial of such issue ( Matter of Rosenbaum [ Amer. Sur., N.Y.], 11 N.Y.2d 310).