dnd 5e – Using pocket sand for the opponent's eyes is considered "free" action?

In the "Other activities in your round "(PHB 190) the rule says … "You can also interact with an object … for free, either during your move or action."

If I pocket my opponent in combat before attacking or running in front of him, is he considered a free or normal action?

And if I hit him with the sand, does the sand blind him, which puts him at a disadvantage?