Does Yasuo wind wall block one direction or both?

Solution 1:

Yasuo's Windwall does block every projectile in both directions: watch this video to see it block form both sides, skip to 1 min 46 secs to see it block from the back.

Solution 2:

Yasuo's windwall blocks in the same way from both sides.

Solution 3:

As an adc main, I can attest that Wind Wall blocks projectiles from both directions. I've had plenty of duels with Yasuo's where we keep running from one side of the wall to the other. Regardless of which side the wall was originally set up, it will block any projectile that attempts to pass through it from either side.

FWIW, Braum's E shield works the same way (it won't help Braum any if he is on the wrong side of it, but it will prevent projectiles from passing through and damaging teammates). I'm not sure if Braum still benefits from the damage reduction if the shield is facing the wrong direction, but I suspect he does not.