Board Thread:General Discussion/@comment-5695542-20131107215511/@comment-10579249-20131125052112

Stefan (Shikai - "Rust & Shatter") wrote: Savalric wrote: Kenpachi is awefully powerful, enough so to scare yamamoto into never training him (fully). I don't think someone who couldn't handle Yamamoto's bankai could handle Kenpachi.

Unohana was playing with Kenpachi down in the Muken, mortally wounding him then healing him over and over, forcing Kenpachi to use more of his hidden powers. That fight took place AFTER Kenpachi's fight with Royd, so he clearly wasn't using his full potential at the time.

And Kenpachi was shackled when Yamamoto feared training him. Although, based on what I read and saw, I cannot say for certain, but it's fairly possible. Kenpachi would've torn a hole through the entire Sternritter (Maybe not bambi) if left unchecked. I doubt Ywhach would've risked him defeating Royd, especially if he thought he was important enough to recruit.