biting and drawing blood for no reason

My 1 1/2 y/o male Akita has all of a sudden started biting and wanting to attack my neighbor when I’m at home. They have been buddies and lately Bear has bitten him 4 times and drawn blood, growled and went to attack him one day and I have no idea why. He only goes up to him and plays when he wants or when I’m not home. When my neighbor goes up by him or calls him he comes by me and looks at him sideways and I don’t know why. He also has become deathly afraid of men but that started about 1 year ago and I don’t know how to get him over it. We even go to home depot to get him around men and still not much progress.
Please help. I love my Bear but hate to get pulled around when he starts freaking out about a guy.

Thank you again,
Rachel