I had a 6 month old GSD attack me. What do you think about that?

Hello, my name's Dean from Australia top site. I owned a German Shepherd who died at the old age of 13 about ten years ago I got him at 8 weeks. He was from old West German bloodlines imported into this country at about 6 months. I was walking him off lead when out of nowhere he launched into a full attack on me grabbing hold of my upper arm and shaking kicked him in the guts but he would not let go. He only had one baby canine left this broke and he lost his grip as I kicked him again he went back about 10 feet looked me in the eyes and came at me again. I was ready and grabbed him by the throat and pinned him on his back with my knee in his chest he was not giving up. I then had to calm him down not letting him up for about 15 minutes. I let him up when he had calmed. He wouldn't come near me for half hour but after that nothing like that happened again. He was a great dog. Also when in prey drive he would have hackles raised. He had a very high prey drive if you didn't throw a ball he would come after you also very possessive. Some people have said he was an alpha dog. Curious on your thoughts.

Regards, Dean melb Aust