He is dominating the dog. Telling he is the dogs master. Even domesticated, dogs are pack creatures and the guy is trying to establish himself as the leader. This can be seen by how the guy straddles the dog, the very same way dogs do in order to dominate over one another. This man takes it to far though. There is obviously no need to be that rough with the dog and it is obvious the dog is in pain. It's one thing to roughly train the dog, it's another abuse it. This man should be fined/jailed and not allowed to own or work with dogs ever again.