Here is the reply I received from baseballhq. Like I said, I'm not much of a stat guy.
Interesting that HR don't factor into the equation.
Actually, not a typo. If you look at the metrics that RandVar measures for hitters (h%, hr/f, and xBA) and compares to actual production, what the +5 is saying is that he got less value out of his 2010 skill set than we would have expected. For instance, look at his .260 BA compared to .330 xBA. When we see that sort of gap, we would normally expect BA improvement to be coming. Similarly, he had a 24% hit rate, compared to prior levels in the upper 20s.
Now, I wouldn't necessarily put a ton of stock in that +5, as some of the modeling that's going on there probably breaks down as you start to look at skills that are as outlying as Bautista's. For instance, the low h% is at least partially due to the fact that HR are excluded from that calculation, so that's 54 hits that he's not getting "credit" for there (since those are not, in fact, balls in play). It's a very unusual skill profile. The +5 is awfully interesting, but not necessarily predictive.
Hope this helps,
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