How could the Moon have arisen from a collision - what would make for an elliptical orbit? One serious theory advanced for the creation of Earth's moon is that it resulted from a collision. 

However matter would be thrown off in all directions and some will fall back. How could a mass of ejecta as large as the Moon all end up travelling together in a single direction and therefore a single orbit? For a spacecraft to attain orbit requires some form of propulsion. Even if the impacting object 'bounced off' I'm still not clear that it could end up where the Moon is and travelling in the right direction. This would require it to be 238,900 miles away and travelling roughly at right angles to the Earth's gravitational field.


  The giant-impact hypothesis, sometimes called the Big Splash, or the
  Theia Impact suggests that the Moon formed out of the debris left over
  from a collision between Earth and an astronomical body the size of
  Mars
  
  https://en.wikipedia.org/wiki/Orbit_of_the_Moon
How could a mass of ejecta as large as the Moon all end up travelling together in a single direction and therefore a single orbit?


The Moon did not form this way. The giant impact hypothesis instead proposes a collision between the Earth and an object that was significantly larger than the Moon, roughly ten times the mass of the Moon. Per this hypothesis, large amounts of material ejected from the surface of the Earth. The energy released from the collision would have heated the impactor and the surface of the Earth immensely. The proto-Earth would have been enshrouded in an atmosphere of vaporized rock. Meanwhile, a handful of Earth radii out, there was an orbiting collection of bits, a few somewhat large, but most rather small.

Over the course of decades to centuries, these bits coalesced to form what would become our Moon. The Earth cooled and formed oceans. The close-by Moon raised huge tides on the Earth. Like today, but amped up by orders of magnitude by those huge tides, the tidal interactions between the Earth and the Moon made the Moon's orbit recess from the Earth. Now we see our Moon at about sixty Earth radii from the Earth, compared to the roughly one tenth of that when the Moon first formed.