Why are craters round?

This seems like a dumb question. When two objects collide at random I
would expect that some of those collisions would be tangential, with one
object skipping or glancing across the surface of the other. Sure, gravity
plays some role to bring objects into direct opposition. But with the speed
and momentum of these asteroids I would have thought that a lot of
collisions would be glancing blows. Shooting stars don't go directly to
ground, they shoot across the sky.

When I look at the surface of a planet or moon I see only round craters.
This is even in those celestial bodies with no atmosphere to deflect or burn
the asteroid. Why aren't some craters elliptical? Is it that the collision
is only a catalyst, and the major energy release is the subsequent explosion
of impacted matter?


Dave