In earlier times players used to put the hands up in a rather static manner near the net while their team is servicing. this *shades* the server from opposition. But according to the changed rule you cant keep a **fully stretched stationary arms** above your head while you are in the 3m box and your team is serving. But still a semi stretched or moving arm is allowed. it might be the referees' will, but most of them agree to it this way.