Well, we would need more particulars, such as what kind of grass, what part of the USA you garden in, whether or not the lawn is fenced in, how big and how deep the craters are, how quickly they appeared, etc. As it stands, it could be anything from sod webworms to your own dog. You might want to repost with more info.

In the UK foxes and badgers dig the lawn for worms. Or did you have a recent meteor shower!!

When I was a kid, I used to pray for that!