The formation of the Moon had many hypothesis over the years, most of them involving a Mars-sized body called Theia, which presumably collided with the Earth. But even within the Theia hypothesis, is not very clear the conditions of that collision. So, what is the most plausible hypothesis about Theia today?
Theia fully disintegrates and the remnants debris form the Moon in a head-on collision(the Big Impact hypothesis)
Theia-Earth suffer a glazing collision and Theia manages to escape to space, but some of the remnants of the collision form the Moon (Reufer, 2012)
Other hypothesis, such a double Theia system
All the hypothesis have problems, but to me the most believable is 2, because it solves the majority of the problems of the other ones, although there's not much consensus on that one, the only who defends it is Reufer.
For example, some research shows that only 2% of Theia actually contributed to the formation of the Moon (I don't remember the reference), so 1 doesn't seem too much feasible because according to that one Theia fully disintegrates.