[Kansas Ref]

Most coaches these days instruct their defenders to "wall up" when applying defensive pressure on a shooter. In that position defender's hands/arms are straight upwards as the shooter tries for goal. A foul is typically not expected to be called in such a contested shot bcz its apparent to everyone that the defender was legally contesting the try for goal. In contrast, when defenders motion their hands/arms go downwards, making a "roof", as the shooter tries for goal we refs are challenged to detect contact--in fact I would assert that a foul is expected to be called. We refs are challenged to instantaneously and correctly differentiate between these two scenarios. Herein lies the challenge in officiating verticality.