The invention relates to a cap (100) for containers for carbonated and non carbonated beverages, of the type used by sportsmen. The plastic cap consists of a supporting element (1) which is screwed on the bottleneck; a pivotal element (2) which pivots by an angle of approximately 120° with respect to the supporting element (1), acting as opening and closing valve for dispensing the beverage; and optionally, a protective cap (3). The pivotal element (2) closes the container in fluid-tight manner. Unscrewing the cap (3) in a certain direction causes the simultaneous pivoting and translation motion of the pivotal element (2), thereby putting the container in communication with the external environment. A kinematic coupling is also provided, which allows the activation of the pivotal element (2) as opening and closing valve by pushing and pulling the vertex of the pivotal element in axial direction, for the cases in which the protective cap is not available.