If you hold the head of the hammer and throw it, the hammer will not spin.
What an incredibly inefficient way to throw a hammer ... and I'm still not sure that's correct (unless you're throwing it straight down; then aerodynamics might keep it straight).
There's a reason not many knuckle-ball pitchers make it to the big leagues. Just sayin.
I'm pretty sure that Thor's hammer is magical. If I ever find a disc crafted by the gods, I'll be sure to let everyone know, so we can stop throwing discs with silly spin, and just let their will take them to the target.