How to track a 3d object to a moving live action object?

Hey all, I’ve used Blender’s 3d tracking system to add 3d objects into live action, but these object were always stationary. How would you add an object such as a spear so that it sticks into somebody and moves with the person as they fall?

Theoretically it can’t be done with one camera view because you have nothing to triangulate on with a moving object whose true position and motion vector are unknown.

However, if (for example) it is a person then you can plot the positions of their feet relative to ground features across all frames and determine roughly where they are standing, then make a good guess as to the position of the rest of the body and thus make a good stab (no pun intended) as to where the spear needs to be placed in 3 space.

It would be just a lot easier to use some form of primitive motion capture (such as using 2 cameras at known fixed locations) to shoot the scene along with your main camera.

Couldn’t you set tracking points over the person’s body and then track them as they fall, accounting for movement as well as rotation? Would that give you enough data or is this way more complicated?