What are you doing, Tristana?
Where did your bones go? You're not Zac.
Where did your bones go? You're not Zac.
Plenty of models do that, even Braum. It's to simulate movement.
In the Yasuo developer blog or whatever gives some behind the scenes stuff it talks about snappy over exaggerated movements like that. It's because it makes it look cooler and more satisfying.