I've thought about implementing a houserule for shields, drawing upon inspiration from TROS combat.

This has as much to do with the difference between a spear and sword as it does a shield

In HM, a spear is a great weapon, makes you wonder why anyone would use a broadsword. After all it attacks about as well (higher AC but off hand penalty), has a higher primaryimpact, and handles armour better.

In TROS the swords come into their own. Why? Because if a shield is used. it provides static defense to the body. And thrusts are less effective both from to hit and damage to the head legs and arms than a swing is.

The only ting with a thrust - it can go vs the often unarmoured face of an opponent, but with the optional favoring rules in helps the defender out here also.

How to translate to HM? I don't like the static defense of the shield in TROS, but I like the way it changes combat. SO here is my idea:

When using a shield, it has a bonus of +20 to defend attacks to the body, but +0 on strikes to the head legs or arms.

If you implement this idea, the arms/legs/body/head zones work far better than low/mid/high

Also, thrusts aiming at the various zones are penalized like this:
Head arms legs -15
Body - 0

Swings have no penalties to the area targeted.

THis makes whields excellent defense to the body, but they still are not static armour as in TROS.

And the sword and other weapons that can be swung do what they do best - lop at arms and legs, the head sometimes also.

The only thing is the head will likley be targeted often by a thrust, and there is not a whole lot to do unless some form of favoring is used. But still it brings back a lot of the effectiveness of something like a sword.

Swords are now effective against someone with a shield and not a lot of limb/head armour, like they were in real life. The head to toe mail eventually caused modifications in swords as the were no longer going after unarmoured body parts.

THere could be some form of favoring added, though this would make things more complicated. Maybe you can declare one of the aimng zones as favored, when the opponent declares his strike a chit or something can be turned over with the favored area. I was thinking something along the lines of you can gain a +10 to your defense of an area, but it's -10 if you guess wrong. You have a 25% chance of getting it right, though lack of armour in an area or a thrusting only weapon can make you guess right more often. You can also allow favoring to +20 for a -20, or +30 for a -30.

Maybe the exact nembers for penalties need to be played with - Is the +20 for body enough?