My sister and brother-in-law adopted a large 5yr old Pitbull who I adore. He is the sweetest dog and for the first few months had few behavioral issues. However, over the holidays he showed some concerning behaviors that has my brother-in-law worried because he has had family members bitten by dogs before. A few of us were talking with the dog by our feet and my dad reached over to grab something near the floor. The dog had been watching him and jumped up at his face out of nowhere (He's a top heavy dog so jumping is not normal for him). Their heads bopped and in the rush it didn't look like there were any teeth bared. He was quickly grabbed and he didn't try to continue. Because he is a rescue Pitbull his ears are cropped and his tail normally hangs really low so it is hard to tell if there were any warning signs of aggression. We wrote it off until later that day he tried the same thing with other male family members. The more concerning part was later that evening when he seemed to fixate on my dad again, following him around which is unusual, staring at him, and waiting for him to bend over. We had to keep him on a leash that evening to keep him from my dad. He has been around my dad and this hasn't happened before. My dad is a soft-spoken guy who mostly ignores the dog with occasional pats. Again, the behavior didn't seem aggressive in the defensive sense-- there was no growling, snapping, ears pinned back. To me who is not an expert, it seemed more assertive. He is fine with other dogs, but does tend to hump I think out of social dominance. As I said, my brother in law is seriously concerned whereas I think it may be an assertive/ humping behavior that requires training. Any advice?