It's not like it's COMPLETELY out of nowhere. 2013 = worst wRC+ since his rookie/sophomore seasons, worst HR total and ISO since that same time, and an ALARMING spike in GB% (I'm guessing groundballs don't turn into singles very often for country breakfast).
But yeah, those are mostly hindsight, post facto indicators. I do think it's fair to conclude that his talent level isn't what it used to be though. Or, something has changed in his approach.
It's like him and the entire f***ing Royals roster have been specifically told to beat the ball into the dirt. They are 2nd highest in GB% in baseball, behind only SDP. Worst ISO in baseball by almost 0.020 points...