A valve for intercepting a fluid in a duct, comprising: - a valve body comprising an annular wall which delimits an internal compartment, in which a fluid inlet and outlet are defined, and a first shoulder and a second shoulder, internally radially protruding from the annular wall, between which a space is defined; - a ball shutter, accommodated with clearance in the space of the internal compartment, having an external surface and being rotatable about a rotation axis between an angular closing position and an angular opening position; - a sealing device (30, 32) placed inside the space, abutting against the respective shoulder (24, 26), suitable for obtaining a fluid seal with the external surface of the shutter; - wherein said sealing device (30, 32) comprises a continuous sealing ring, made of polymer material, placed in contact with the external surface of the shutter, and a continuous support ring, made of metal material, coupled to the sealing ring and placed between said sealing ring and the shoulder (24, 26); - wherein the support ring comprises a continuous annular coupling portion connected to the sealing ring and a continuous annular influencing portion joined to and elastically bendable with respect to the coupling portion to provide an elastic lever between the sealing ring and the shoulder (24, 26); - wherein the coupling portion comprises an annular contact portion formed by a frustoconical wall; - wherein an outer wall of the sealing ring is at least partially in contact with the side surface of the annular wall; and - wherein, in an emergency condition, in which the sealing ring is absent, said contact portion is in contact with the external surface of the shutter at least due to the pressure of the fluid, thus obtaining a fluid seal. - a valve body comprising an annular wall which delimits an internal compartment, in which a fluid inlet and outlet are defined, and a first shoulder and a second shoulder, internally radially protruding from the annular wall, between which a space is defined; - a ball shutter, accommodated with clearance in the space of the internal compartment, having an external surface and being rotatable about a rotation axis between an angular closing position and an angular opening position; - a sealing device (30, 32) placed inside the space, abutting against the respective shoulder (24, 26), suitable for obtaining a fluid seal with the external surface of the shutter; - wherein said sealing device (30, 32) comprises a continuous sealing ring, made of polymer material, placed in contact with the external surface of the shutter, and a continuous support ring, made of metal material, coupled to the sealing ring and placed between said sealing ring and the shoulder (24, 26); - wherein the support ring comprises a continuous annular coupling portion connected to the sealing ring and a continuous annular influencing portion joined to and elastically bendable with respect to the coupling portion to provide an elastic lever between the sealing ring and the shoulder (24, 26); - wherein the coupling portion comprises an annular contact portion formed by a frustoconical wall; - wherein an outer wall of the sealing ring is at least partially in contact with the side surface of the annular wall; and - wherein, in an emergency condition, in which the sealing ring is absent, said contact portion is in contact with the external surface of the shutter at least due to the pressure of the fluid, thus obtaining a fluid seal.