Four 1st level PCs fall into a pit. One of them is magically possessed (i.e. such as with a Crown of Madness) and begins attacking the other party members.
Ideally, the party would like to restrain the PC without damaging them so that when they escape they have enough hit points to survive the rest of the dungeon.
In real life, we might use a headlock or some other restraining moves like one sees commonly in wrestling matches. (Our emergency department security team regularly restrained aggressive or psychotic patients with one person taking the head and thorax and others each taking a limb.)
But there seems to be few moves that restrict actions in 5e like we would see in wrestling commonly. Grappling still allows a PC to attack or cast spells. Use the Shove action to push someone Prone and they still can attack or cast spells.
In the absence of ropes, manacles, or magic – what can first level PCs do to restrain a possessed character without damaging them significantly? Is there anything in-game that matches what we see in wrestling matches today?
(To clarify: By "restrain", we mean the layperson definition as in “to prevent from attacking” (like in wrestling) and otherwise restrict their actions – not the in-game "Restrained" condition, which still allows attacking and casting spells.)
Best Answer
This is one of those times the DM needs to ignore the rules.
A DM has huge leeway to ignore the rules and do whatever feels right. In this case you would tell the DM what you want to do "I grab his arms, player B grabs his legs and player C sits on top of him as we pull him to the ground" and the DM decides if it works and what checks are needed (I would rule some kind of strength contest with advantage to the party for teamwork).
Just because there isn't a specific rule doesn't mean that it cannot be accomplished and the rules generally are not written for PvP so situations such as this are not fully covered.
Similarly I would let this kind of thing happen in real combat, but using the rule of cool it would only happen when appropriate, and only once. It wouldn't be something I would let you get away with very often.
Using the fully defined rules (If you don't count rule zero as a real rule) I am not sure there is anything that specifically covers this, so your DM could say it is not possible and grappled is your best bet without magic.