That's a work in progress Vroom, and you can't imagine the mess it is to balance.
I got answers from my arms master and i made some reseraches.
Shields are either meant for fighting in formation or for melee / duel fighting.
The former type is usually firmly strapped tothe arm or even the body of the fighter and it is useless to try and disarm them. But you can use it to have a wrestling hold on your foe. You can also use your own shield to use as a lever and pull the opponents shield in such a way that the fighter ext to you might have a strike at him. Hooking weapons like axes, spiked maces, hooked spears, boar spears, most pole weapons and many etc.. could be used to violently pull the shield and harm its wearer. Simply hacking at the shield can be a solution if the it is in plain wood. Plywood will resist to nearly anything you send at it (save siege weapon ammunition and several axe blows, i believe one may actually stop a bullet fired from a handgun but i may be wrong). Metal shields will bend or just "ring" (actually vibrate to evacuate the energy of the blow). Wooden shields with a metal rim will prove hard to hack, and those with a soft wood rim will trap weapons trying to do so.
Spears can be used like levers to force their way under a shield and strike the elbow or arm pit.
In melee or duel fighting, the shield is actively used by its wearer to parry incoming blows. Those shields are lighter and usually more maneuverable than the ones used in formation. According to my arms master (and i think he is right) there is no point in losing time to remove a shield because if you are able to do so, you'd better do it to the main hand weapon. Worst of all, some dueling shields had sharp rims, or spiked ones. You don't want to come too close from them. Last, disarming a shield involves using your weapon to take an hold on it. If you can do this, you also can plunge it in your foe's body.
If you don't have any weapon, you may want to disarm your foe bare handed (he showed us hos to do on several occasions). If the shield is simply hand held, it is possible to remove it. If the shield is strapped to the arm or body, you can use it has a wrestling hold.
However, it is very unlikely your foe will let you do this. If he has a weapon you are dead meat. Better to disarm the weapon or use it as a wrestling hold, or grab it through a locking hold (this has also been demonstrated in today's lesson).
Don't know yet how to represent it in the rules, but i think rolemaster already has everything necessary to represent accurately shield maneuvers, disarms or wrestling. We just have to adapt it.