Stat dorks take:
But now we come to the catch, which is that the numbers Balfour has been enjoying over the last two seasons simply aren't made to last.
The .229 BABIP Balfour has compiled is way too good to be true, especially in light of that 23.3 line-drive rate. His career rate says he's more of a .260 BABIP guy, and that's the range he eventually ended up in last season after his BABIP inflated from .237 in the first half to .305 in the second half.
Per FanGraphs, the Steamer projections for Balfour see a .298 BABIP in his future for 2014. That seems all the more likely now that he'll be pitching in the AL East rather than the AL West, and there's another thing about that switch that could burn Balfour.
Consider these home/road splits from Balfour's time with the A's:
Balfour's 2011-13 Home/Road Splits
Split GB/FB FB% HR/FB
Home 0.93 40.3 8.0
Road 0.85 43.3 10.0
It's not totally significant that Balfour gave up a few extra fly balls on the road. What's really significant is that more of the fly balls he gave up on the road ended up going over the fence.
And that isn't all that surprising. Balfour was playing his home games at a huge ballpark in O.co Coliseum, after all. According to ESPN's Park Factors, it was the No. 25 home run haven in MLB last season. That's pretty much par for the course with Oakland's home park.
To boot, Balfour's road splits were likely saved from further harm in regular action at Safeco Field and Angel Stadium of Anaheim. Up until the Houston Astros brought Minute Maid Park into the mix, Rangers Ballpark in Arlington was the only home run haven to be found in the AL West.
Balfour is headed to an entirely different situation in the AL East. He's been a member of the division before, sure, but at its one and only pitcher-friendly park in Tropicana Field. Rogers Centre, Yankee Stadium and, yes, Oriole Park at Camden Yards were among the 10 best home run havens in 2013. Fenway Park wasn't, but it was a top-10 home run park as recently as 2012.