If I'm following the author's argument, he's claiming that Starlin's low babip, and by extension poor performance in 2013, can be attributed to a new swing that brought about a dip in his contact rate on balls in the zone. Leaving aside whether or not Castro's swing really changed that much, two criticisms occur to me. First, what does contact rate have to do with babip? And second, Starlin's Z-Contact fell from an average of 92.6% in 2010-2012 to 89.2% in 2013. That's not entirely negligible, but it isn't much either. In his three full seasons, Castro saw an average of 2577 pitches per season. Using that number (for purposes of comparison) Castro swung and missed at about 23 more pitches in the strike zone in 2013 relative to his 2010-2012 rate. Even if you assume all those balls would have been put into play if struck, and furthermore that about a third of them would have fallen for hits, that still only gets you to about a .258 average. Am I missing the point?