Dog acting differently?

I am 8+3 and I swear my dog knows something. He has been overprotective (sleeping right in front of the front door and barking/growling at everything walking by). Yesterday when I was walking him, a group of teenage boys walked by, being loud, play punching each other, etc. Not bothering anyone, just being typical teenagers. My dog growled at them and jumped on the one boy who was play punching! He never jumps!
And, he's been laying next to me with his head on my stomach, which he never does. I swear he knows something's up.
Is anyone else experiencing anything like this?