User blog comment:Zathronas/Analysis by an author: Volume 2 episode 11: No brakes/@comment-3146930-20141024021616/@comment-4010415-20141025143629

... Basically, my view on Yang not using her semblance during the Neo fight is this...


 * First off, just gonna point out, Lindsay said that Yang's hair is the source of her power, kinda like in the tale of Samson and Delilah. I think that means Yang stores the energy for her semblance in her hair, and therefore, it makes her very defensive of her hair. That's her power meter. Shorter power meter means less room to store energy, which means smaller cap on the amount of energy she can put into an attack, which means weaker "big" attacks. That storage is why she could use her semblance on the Ursa without having been hit.


 * I'm sure Yang can willingly activate her semblance, so it's not like her meter is gonna reach supercharged level and then activate automatically. Therefore, obviously, Yang fully has the ability to use her semblance strategically...


 * ... which is what she does, as long as you don't damage her hair. If you damage her hair, that's her rage button, and she loses logic about conserving energy. As was said in this thread of replies, Neo was dodging like crazy, and when she couldn't dodge, she completely and effortlessly blocked attacks with her parasol. Using her semblance would be useless.

"Why didn't Yang use her semblance anyway, despite that?"

Because it wouldn't do a damn thing against Neo if she can't hit her, and she knows that. She may be the brute force fighter of Team RWBY, but she's not fucking stupid. She knew it would be a waste of time and energy, and that energy could be better used if she managed to somehow get the upperhand on Neo.