There are several critical speeds during the takeoff roll that have to be determined. Vmc, the minimum controll speed for flight in the event of an engine failure, usually dictated by available rudder control.
Vmu, the minimum unstick speed, where the airplane can be lifted off. This is where tail strikes can occur due to the geometry of the fuselage, since the nose up angle (angle of attack) for maximum lift can exceed the maximum physical nose up angle to the runway.
In actuality, Vmu could equal the stall speed, Vs, if not for geometric limits of the nose up angle. But lateral control could be a problem there.
Other factors such as runway length are involved with other speeds, V1, etc. And these speeds are dictated by other factors as well, such as weight, density altitude, etc.
From what I heard, the pilot was not aware of the tail strike, only that he may have hit something.