Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
I would suspect that there is a dominance issue with your puppy and other dogs. The best thing that you can do to curb this bad behavior, is to:
Purchase a DAP Collar at the pet store. This is a canine pheromone that acts as a calming agent to help your puppy past this.
Take your puppy to obedience school so that when these episodes occur, the puppy will listen to you and you can discipline him.
Have your vet examine your puppy to be sure there is not a medical cause for this and be sure that eh is neutered since the hormones will tend to make him aggressive.
If none of these work, your vet will have medication to help train your puppy out of this bad behavior.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, ***** *****