Traditional knock down Karate is very different from Shidokan Karate tournaments. For example, in Kyokushin grabs, throws, take downs, and submissions are not allowed.
In Shidokan Knockdown rules grabs, throws, and subs are allowed. The rules allow brief moments of grabbing/grappling to emphasize speed and control to finish an opponent under a knock down format. Remember all knock down karate rules seek to finish an opponent in the most efficient manner possible, creating a sense of urgency.