Now that MC-269601 has been fixed, players around the smash attack area of effect can now be knocked back. However, despite players shielding into the direction the knockback was sourced from (the smash attack that was performed), the knockback is not mitigated in any way, unlike how knockback from other sources is mitigated successfully, such as explosions which are also AoE.

There's another similar issue regarding wind burst, currently reported in MC-270214.

How to reproduce

You need two players to reproduce this.

1. Equip a shield, and tell your friend to equip a mace.
2. Summon an armor stand, stay close to it.
3. Tell your friend to perform an smash attack into the armor stand.
4. Before your friend hits the armor stand, stay blocking with a shield while facing the armor stand.
5. Notice how the knockback from the smash attack isn't mitigated at all, despite blocking with a shield.

Expected result

The knockback from the smash attack would be mitigated when the player is shielding, similar to how knockback from explosions are blocked.

Observed result

Blocking with a shield doesn't have any effect, and the player is pushed far away.