Rugby < Football
Look at Jarred Hayne? The Hayne plane hasn't taken off, he can't handle a football right. You could get an NFL linebacker and start him in rugby. NFL player hits are much harder that's because the tackling method concentrates to a smaller area.
NFL you lead in with your shoulder to their chest and head should go to the side. Rugby you want to lead with your arms to wrap them up. That's the focus of the tackling, you can talk about the padding in football but it makes the hits actually harder and players are much tougher. Ask Hayne that one too.