dropping like a stone

And the Angels are dropping like a stone, so we'll probably play them in the first round. The Indians won game one of their wacky home-and-home in-one-stadium double dip. I've got game two on Gameday right now. Through two innings, the Mariners had five of their first nine batters reach base. They scored no runs.

What does dropping like a stone mean?

Thanks!

I plan to learn that next year during my sophomore year when I will change my username to not-so-N2G

Thanks, GG.