There could be one of several possibilities causing this behavior
One possibility is that since Geezy runs with a pack, and is probably the lead dog of the pack, he is acting like an alpha male, head of the pack dog, and running off anyone he sees as a threat. If this is the case, letting him run loose, and do as he pleases whenever he pleases will only reinforce him to act this way. Spanking him, or yelling at him, will do nothing to change him, and may even make it worse.
Another possibility is that while you were away, something happened to cause this behavior. He may have had an incident with someone on your property; he may have been frightened by fireworks; he may have had an incident with another dog.
We will probably never know what started it, but now that these attacks are happening, they will only get worse, unless you change him. The first time he attacked, he may have found that it was fun or rewarding for him in some doggie sense, and now he will continue to do it. The only successful treatment for behavior problems is either training
, behavior modification, or both.
First of all, he must not run loose and do as he pleases whenever he pleases. You may need to start keeping him inside when you are home. It probably would help to take him to an obedience class, and work with an experienced trainer on this problem. You will have to train him to accept strange men, and reward him for doing so. This should be done in a controlled, safe environment, with an experienced dog trainer.
This will escalate as long as he runs loose with his pack. If he is getting rewarded for the attacks (people running away is a reward for him), he will keep doing it. Yelling at him, or spanking him only confuses him; he probably does not understand that he is being punished for the attacks. Negative reinforcement like spanking and yelling rarely trains a dog to do anything but be afraid of you; dogs learn by being rewarded for good behavior. You need to train him to do what you want him to do.
This is a tough situation, because someone could get hurt. Until you get help with training him, he should be kept inside or in a kennel.
Good luck with Geezy. Rebecca