User blog comment:Zolnir/Flaw in Tournament Setup/@comment-5414218-20160317123214

Oobleck couldn't have stopped Yang from attacking Mercury because he right next to her and it was completely unpredictable for everyone, even more so to him that knows Yang. No-one could have, even Ozpin didn't stop an arrow flying to the target he was meant to protect and that was right next to him because he didn't expect it.

Saving Penny is even more unlikely because it was part of the fight.