Quote Originally Posted by Buffalobiian
I've always wondered, Koh's pretty awesome at batting, starting at a much younger age than when he trained for pitching. He goes to bat occasionally, even if it's for the odd sock that he broke, but it's not even close to getting as much attention as his pitches. I don't think Wakaba ever said anything about liking baseball neither. All she told him was Aoba's training methods... nor did she tell him upfront that he "should" be a pitcher.
The 'past' scenes are a little jumbled here since everything is being seen as flashback, but in the manga it was the full first volume.

When Aoba asked Koh why did he had to join baseball he said "because I once saw a very cool pitcher". He was obviously referring to Aoba and a scene from where they were kids. This scene was shown on the 2nd episode I believe. Wakaba afterwards gave Koh Aoba's training method.