The parallels between rugby and football are very interesting, particularly when it comes to tackling. In football, players treat themselves like missiles; in rugby, however, they operate far more like animals trying to bring down another animal, using their arms and bodies to absorb movement and contact. What results are big hits that look and feel different and a game that is more fluid and dynamic.
Because the tackler here was immobile when he made the hit, the collision is far less dangerous than it would’ve been had he come sprinting at the ball carrier. This is why football can be so treacherous and injury-prone; when superior athletes are constantly sprinting all over the field, there’s a lot of physics going into those hits — complicated physics. Contrary to that, this is just a solid piece of mechanically-sound tackling, and, as you can see, it’s just as effective as it would’ve been had he come flying out of nowhere.