Yeah that type of aggression has nothing to do with tug. Often it’s genetic or environmental like something happened to make him fearful.Someone would actually try that? If my dog was guarding his food, there's no way I'd be putting my hand near it. Because a lot of dogs are protective around their food, I try to avoid going near their food while they're eating. Most I'll do is pet them while I tell them how good they are, or put more food in their bowl if they didn't have a full serving when they began. Because my dog often drinks his water after he eats, I'll sometimes refill his water bowl while he eats too. (My dog has zero aggression when it comes to his food or his toys. If one wanted to, they could literally take his stuff right out of his mouth with no problems. He's just untrustworthy around certain people that he might not be familiar with and no where else.)