I unfortunately do not have a very complete answer, but partial answers are worth something, I suppose. There's some discussion here about a sword vs. spear bout that reminds us that, outside of movies, it's not that easy to just knock a spear down and keep it there.
I think the hard part is actually grabbing the spear without getting impaled on it. Look at the ranges they stand in: for the most part, it's the point of the sword to the point of the spear, and that's for good reason. The spear guy can easily plunger the spear forward, so by the time your hand is in range of the spear, you're probably fucked.
Batting the spear down is not an easy task either. There's not much of an angle to do this at all, and even if somehow you got it down, he can draw the spear back rather quickly. In a lot of these bouts, the spear guy gets 2-3 solid hits in before the kendo guy can even get in range to do his one hit.
This is further reinforced in the test that Lindybeige did at a HEMA event where you can repeatedly see that the stabs are quick and high. Deflecting them is less a matter of "drive them into the ground or into the air" and more "move them enough that they barely miss you".
We did do a step disarm when I was studying Bujinkan in Dayton, OH, but it was in staff vs. staff combat, and was intended to be done after grappling with the person and more or less immobilizing the spear before stepping on it. It was difficult to target the spear with your foot without looking and was tricky balance-wise, but indeed, it didn't take much weight to rip the staff out of the other person's hand, essentially doing a third-degree lever effect.