Xander............
Looking at his plate discipline numbers on his BP player page, it’s pretty clear why this is happening. Bogaerts is simply swinging at more pitches. After being almost too patient last season, it appears that he is overcompensating this year. His overall swing rate has risen about 4.5 percentage points. A big part of that is swinging at more pitches in the zone, which is a good thing. Unfortunately, he’s also chasing a lot more pitches out of the zone. This kind of approach hurts his power numbers as well as his walk numbers. Instead of whiffing on these bad pitches he’s swinging at, he’s making contact on 69 (nice) percent of them, leading to weaker overall contact.
Here's the article.... http://boston.locals.baseballprospectus.com/2015/09/17/this-isnt-xander-bogaerts-breakout-season/