In my new campaign I am allowed to choose one uncommon magic item, and was considering the Immovable Rod:
This flat iron rod has a button on one end. You can use an action to press the button, which causes the rod to become magically fixed in place. Until you or another creature uses an action to push the button again, the rod doesn't move, even if it is defying gravity. The rod can hold up to 8,000 pounds of weight. More weight causes the rod to deactivate and fall. A creature can use an action to make a DC 30 Strength check, moving the fixed rod up to 10 feet on a success.
I was also reading this answer to a previous Immovable Rod questionWhat happens when an Immovable Rod is activated while in a vehicle?, which got me thinking:
Can an immovable rod be used to pin an enemy?
My idea is to use the immovable rod as a staff of sorts, with the added ability of being able to pin enemies. Here, when I say pinned, I mean being stuck under the rod in a restrained, prone position (thanks, nitsua60). Let's simplify the situation too and just assume that the pinned enemy won't or can't just push the button to release the Rod, so we can focus on whether it can be done at all in the first place.
Based on the description I don't see why the immovable rod could not be used to pin enemies, though I'm not sure what the mechanics would be (ie minei.e., my and my enemy's relevant checks) to using the rod to pin (and immobilize) an enemy.
I'm willing to accept answers that can cite RAW one way or the other, or alternatively, any errata or other sources (ege.g., Sage Advice) which would help clarify whether or not the immovable rod can be used to pin. A comment asked whether real martial arts knowledge is okay as evidence: I suppose martial arts knowledge would be appreciated as additional support/justification for an answer about why using a rod to pin would/wouldn't be possible.