I believe Adi has the correct way the rule is written. The thing is they do consider it a hand ball if you put your arms up when you know a player is about to strike the ball and it hit your arms whether you see the ball or not. This is where the unnatural arm position comes into play. If I am rushing out to block your shot, and I jump turn my back and my arms go up, the ball strikes my arm, it's a hand ball. If I rush out turn my head and my arms are pretty much by my side, the ball strikes my arm, not a hand ball. Confusing, but hey, lets talk about the offsides rule. That one is a bit more interesting.