Were Arsenal right to be 'fuming' with refereeing after Atletico draw?

We've had two nights of handball controversy, first involving Bayern Munich and now Arsenal. In both cases, the ball took a deflection off the body before hitting the arm, and fans have been conditioned into thinking this means there cannot be a penalty. What referees actually look for is a clear change of trajectory. Why is that? Because it means the arm position would not create a barrier to the natural direction of the ball. …