Our approach to rating players has always focused primarily on performance, as opposed to scouting reports and reputation. Scouting reports are professional opinions about current and future skills, and they are useful.
Many players have reputations that accurately reflect how well they have performed.
But sometimes there's a big difference between a player's skills and reputation, on the one hand, and his performance, on the other. Our job is to rate a player based on how well he performed in a particular season. So we look for ways to accurately measure each player's performance. When looking at how well a pitcher or catcher defends against the stolen base, it's not all that easy to find relevant information that is publicly available. That's a good start, and it helps, but it's not enough.