A thin spherical shell lying on a rough horizontal floor is hit by a cue in such a way that the line of action of force passes through the centre.so there is no torque and it moves with a linear velocity V and no angular velocity.the linear velo is to be founded when the shell starts purely rolling. now the question goes whether the principal of conservation of angular momentum is valid here.i don't think so because an external torque due to friction will be acting on it. [. The shell will move with a velocity nearly equal to v due to this motion a frictional force well act in the background direction, for which after some time the shell attains a pure rolling. If we consider moment about A(the point of contact with the floor), then it will be zero. Therefore, Net angular momentum about A before pure rolling = net angular momentum after pure rolling.] This is what my textbook says but it makes me wonder.