why is tank yasuo not played
rush shiv and ie into full tank
flow shield helps you tank even more and wind wall projectiles that will hurt you
example build
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maybe add in steraks if you're ahead
rush shiv and ie into full tank
flow shield helps you tank even more and wind wall projectiles that will hurt you
example build
/ 
maybe add in steraks if you're ahead
Well ask yourself this, if you're looking for a tank that still does a good amount of damage. Why is yasuo better than

bronze detected
on a serious note, if he were to do that he will be way more useless in late game which is the part where he shines at, he has no life steal to be able to outtrade or have any outplay potential at all, while his -10% crit damage along with randuins will fuck him up even more, while without last whisper he wouldnt do jack shit to tanks or be able to 100-0 adcs or any other enemy teams with just 1 damage item LOL
Maybe he is just not in the meta
Won't really do enough damage. Yeah you crit, but once people build some armor against you, you aren't going to be doing much against them
The reason tank/bruiser Yi and Fiora are viable is because of the true damage they have. It gives them reliable damage no matter what so they can focus more on building to survive and keep doing that true damage to everyone.
Yas needs to build damage to be relevant. Yes he gains armor pen on his ult (not sure how much off the top of my head), but he still won't be doing diddly to anyone but the squishiest of squishies. And even then it won't be enough to be a viable option.
because he will not do very much damage
You should try out Triforce + PD Yasuo.
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Well yeah but he would not put out that much damage as a regular build that would be more of a my team needs a tank build. And yeah Olaf is VERY annoying even though he is a tank.

There is only death, mine or yours!