Q:

Should the damage from an unarmed strike be reduced by Heavy Armor Master?

The Heavy Armor Master feat (PH p.167) grants the following benefit:

While you are wearing heavy armor, bludgeoning. piercing, and slashing damage that you take from non-magical weapons is reduced by 3.

Recent errata to the Player's Handbook changes the definition of an unarmed strike:

Unarmed strike doesn’t belong on the Weapons table.
Instead of using a weapon to make a melee weapon attack, you can use an unarmed strike: a punch, kick, head-butt, or similar forceful blow (none of which count as weapons). On a hit, an unarmed strike deals bludgeoning damage [...]

Should the damage from an unarmed strike be reduced by Heavy Armor Master?

A:

Yes, Heavy Armor Master should reduce damage from unarmed strikes.
Back in June, Jeremy Crawford stated that the intended Errata which will be released eventually with the next Monster Manual will clarify that all instances (for example) of "bludgeoning damage from non-magical weapons" to instead read "resistance to nonmagical bludgeoning damage" and for lycantrhopes, that would read "nonmagical weapon attacks.", instead of "nonmagical weapons"
See here for the full conversation.

A:

No, not anymore.
The changes in the errata remove Unarmed Strike from the weapons table and explicitly outlines punches, etc. as not weapons.
Heavy Armor Master only reduces damage from weapons, not all sources of nonmagical bludgeoning, piercing, and slashing damage.
As an example, Heavy Armor Master does not reduce the nonmagical bludgeoning damage taken from falling more than 10 feet.
Is this intended?
I doubt it, but Unarmed Strikes are still weapon attacks, and thus qualify for divine favor and the monk feature Stunning Strike.  Heavy Armor Master could easily include Unarmed Strike by changing the wording from "nonmagical weapons" to "nonmagical weapon attacks".

