While either feeding it or trying to knock it out to tame it, it is best to go from underneath it, but closer to its neck then his tail so it doesn’t start turning around and just stays in one spot, trying to hit you but continues to miss
When taming to make it easier stand against a cliff or a good sized rock. I tamed one for my brother and it was a piece of cake with that technique. Also if you find that the place you find the diplodocus isn’t safe just get near it and lead it away. They won’t hurt you they just like to swat you around like they are playing a game of soccer.