The big fat red flag is his strikeout rate. But what's that composed of?

He's swinging less at balls outside the zone than last year, but still higher than his extremely low career average. Still, not much change.

He's swinging less at balls inside the zone than last year, and all told, he's just plain swinging less. Down about 2% from his career average. Interesting, but it's probably driving his current high walk rate more than his strikeout rate - though there's likely to be an impact there as well.

His contact percentage with pitches outside the zone has more or less nosedived. That's... a problem, but it's less so for a player like Mauer who rarely swings at pitches outside the zone anyhow. Mark it, but not as the ONE BIG THING that has driven the strikeouts.

His contact within the zone is basically identical to his extremely high career marks. That's probably good if you're hoping for a bounceback, because swing and missing at pitches in the zone is a sign of ability to get the barrel on the ball declining.

So, all told on swings, we're seeing less contact - mostly driven by way less contact on pitches outside the zone. But still a high percentage of contact that means Mauer's new strikeout rate isn't solely a product of flat swings and misses.

All told, this looks like he's having some problems with balls called for strikes that he thinks are balls. On an eyeball basis, I'd say that I've noticed that too. A lot more pitches down and in that he's not biting on that are being called strikes combined with a continuation of 2013's trend where he'll expand the strikezone up when he's behind in the count. There's nobody I'd trust to figure out and solve this problem more than Joe Mauer, but if there's actually something changed physically (which the above numbers don't necessarily indicate) then we may not see that happen. The only thing left is the batted ball data, which explains his lack of power (fewer flyballs and more groundballs) but not his lack of Mauer-ian singles and doubles because his linedrive rate is typically excellent.