Everyone knew Castro can hit -- he was the youngest player in history to lead the National League in hits with 207 at age 21 last season -- but Epstein wondered if Castro was capable of playing shortstop at the major league level.
"Being around him now and seeing the kind of kid that he is and seeing some of the progress that he's made defensively, (I) actually have even more conviction about his importance to us and the fact that we're going to build with him and build around him in a certain sense," Epstein said Wednesday on "The Waddle & Silvy Show" on ESPN 1000. "He is 22. To me the biggest issue coming in to the season was can he play major league shortstop? We felt like he was gifted enough physically to do it, and he would have to make a few fundamental adjustments. There were some high-profile examples of him losing focus so we wanted to get a handle on that.
"He hasn't been perfect but for the most part he's made the fundamental adjustments that we've asked. He's moving his feet much much better, especially on routine ground balls, and really to me looks outstanding at shortstop. He's still had a couple of instances where he's lost his focus. That's going to continue to be an area of emphasis for him, but this kid cares, and I'm convinced that he's going to get there and his tools are going to show up consistently on an everyday basis as he refines his mental game.
"I think we've go the right answer, the answer we were looking for to playing shortstop fundamentally at the big-league level."
Castro has hit .300 or better in both of his major league seasons and is batting .302 this season. But he has struggled even more with his plate discipline this season, drawing six walks against 43 strikeouts with a .320 on-base percentage.
"At the plate he's a work in progress," Epstein said. "He's going to be one of those kids who gains discipline as he moves into his prime. He's still five years away from his prime. Twenty-seven is the age which most players reach their prime in the big leagues. As he starts to hit for more power, which will happen as he fills out, he's going to be pitched to more carefully. It will be on him to make that adjustment and be a little bit more selective at the plate. You'll see his slugging and on-base increase.
"I'm convinced this kid is going to be a really really good player for us."
Cubs president Theo Epstein joined "The Waddle & Silvy Show" on ESPN 10000 and discussed his team's rough start, Starlin Castro, Jorge Soler and more.