Honestly I don’t think Yuu failed at taking over the pitcher or anything like that. He’d definitely react more strongly to it if that were the case. What really makes me curious is how Nao explicitly stresses that the opponents are the test subjects. I’m inclined to trust her on this, because why would she lie about it?
It is a possibility that Yuu using his power on someone ‘influences’ them in some (permanent?) way. Either that or she was just observing the immediate reactions of the guy and his team.