There are a few problems with that. The first thing being throwing something toward the Earth won't mean it impacts Earth. This is not how orbits work. In order to get from the moon to the Earth, you have to throw it in the opposite direction from the moon's velocity.

But ultimately that velocity is going to be very high. The moon orbits the Earth at about 3,600km/h and you'd have to throw that hammer at a good percentage of that velocity in order to lower the hammer's lowest point in its orbit so that it would hit the Earth. This is just something orders of magnitude beyond what a human being can do.

Edit: If you could do what you're suggesting then we'd already be mining the moon. The biggest problem with mining something like the moon is getting fuel to return the material to Earth. If all it took were a human-scale toss to return to Earth then we'd be hurling minerals our way like there's no tomorrow.