[Exhibitman]

No, it is because of a series of court rulings on free speech that grant certain speech and assembly rights in public spaces, like malls or the walks in front of grocery stores. The purpose of the waiver [it is not an exculpatory clause disclaiming liability but a contract clause waiving a right, so it is a waiver not a disclaimer] is to preclude a 1st Amendment argument that the stadium is a similar public space in which certain Constitutional rights might exist.