The giants of Skyrim are people you simply don't want to mess with. You can kill all the damn dragons you want, but nothing can prepare you for the sheer power of a giant. This video serves as a testament to that.
You see the above image? Yeah, that's a couple of giants surrounding an extremely unfortunate guard; a guard just trying to do his job, you know. You might think that the moments after this will see said guard dead on the floor, but no. This guard's planet needed him, so he flew. Flew like a bird.
Oh, and the other guard that gets hit is just weird, that's why he flew.