Castellanos, from the scouting reports I've read, was quite raw at 3rd. He had the potential to be average defensively, but with him playing in the OF over the past year+, it's definitely a wonder on if he can jump back and be decent right away. I'd err on the side of caution with him. Even if his bat is MLB ready, I think he wouldn't hurt spending the beginning of 2014 in AAA practicing either OF or 3B (but for the love of god pick one, plz).
As for the trade, like it. Don't love it (Kinsler is essentially a faster Infante) but you can't be mad at getting out of some of that contract.
As for the trade, like it. Don't love it (Kinsler is essentially a faster Infante) but you can't be mad at getting out of some of that contract.