When a snowball is thrown at someone wearing armor will cause the armor to take damage and not the player.
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I believe this is an intended feature.
kumasasa
Duplicate of MC-3179
Torabi
But should snowballs cause damage to armor, when they don't do any damage to players? That's what it sounds like the report is saying, but I'm not sure that they do.
Snowballs don't give any damage to players; only certain mobs like endermen or blazes are.