In 2014, Joe Mauer pulled nine percent of his fly balls, according to StatCorner. That was the lowest figure in MLB. The second-lowest figure was 12.3 percent. In fact, that 2014 figure for Mauer is the lowest anyone has posted since 2007 (at least). In fact, Mauer has three of the four and four of the eight lowest shares of pulled flies in single seasons since 2007. This is who Mauer is: an opposite-field hitter with a patient approach and no desire to get out of his comfort zone at the plate. That is, generally, good advice, and it’s made him a Hall of Fame player. Mauer has nothing to be ashamed of. He’s been a star, and he takes a professional approach to the plate.

It has to change, though.

It has to change, because Mauer’s approach isn’t really working anymore. The bottom of the strike zone has grown significantly over the past four seasons. In 2014, that phenomenon only accelerated. For the six-foot-four Mauer, that has led to many more called strikes on pitches low in and beneath the rule-book zone:

Joe Mauer, Pitches Taken Low in or Below the Strike Zone

(h/t baseballsavant.com)

and more called strikes on would-be balls, in general:

Joe Mauer, Percentage of Pitches Seen Outside Strike Zone, Taken for a Strike

(h/t StatCorner.com)

Obviously, while neither Mauer nor any other hitter is to be blamed for poor calls made against them, the new reality of the zone favors aggressiveness. (Free-swinging Pablo Sandoval, notably, has not seen his strikeout rate rise in lockstep with the league, as Mauer has.) Mauer is among the league’s most patient hitters, and so has suffered disproportionately from the growth of the called zone. Thirty-six percent of Mauer’s pitches seen came while behind in the count in 2014, according to StatCorner. That’s nearly the league-average share, but a career worst for Mauer.

To trace back to the fact that led off this article, Mauer went the other way more than ever in 2014.

(h/t FanGraphs)

There are two compelling possible explanations for that:

1. Because he faced so many unfavorable counts, Mauer was thinking and swinging defensively; or
2. He was physically limited, lacking explosion, unable to attack the baseball due to poor health.

I think there’s some evidence in support of each conclusion. On tape, Mauer did often look physically compromised at bat. He would sometimes spin off the ball, striding his way open instead of striding straight and twisting his hips open; and sometimes get stuck, his foot down too soon, his hips and torso stiff, unable to rotate through the ball. Frankly, he looked slow.

At the same time, he clearly hit the ball the other way more often with two strikes on him:

(h/t baseballsavant.com)

and he was worse with two strikes against him than he’s ever been:

Joe Mauer, Batting With Two Strikes, 2012-14

(h/t baseball-reference.com)

Part of the issue here is Mauer’s rising strikeout rate. The better one is at making contact and avoiding the punchout, the better one’s two-strike stat line is going to look. Another partial culprit is bad luck on balls in play:

Joe Mauer, Batting With Two Strikes, 2012-14

but the contact rate tells most of the story.

Zooming out, that’s the big-picture lesson here. Overall batting value consists of four skills: plate discipline, contact rate, pure ball-striking ability and power. I list them in that order because that’s the order in which they take their turns shaping a hitter’s production. Mauer has excellent patience, guaranteeing himself a healthy share of walks and a strong on-base percentage. Unfortunately, that patience has become a double-edged sword, thanks to the aforementioned strike zone growth. Contact rate creates the constraints, the parameters within which batting average fluctuates according to the whims of BABIP (and the batter’s ability to hit the ball hard; it’s not all blind luck, of course). The biggest change in Mauer’s performance is this one. He still strikes the ball well, gets the barrel to the ball, covers the plate well. He just swings and misses more, and that shifts the endpoints of his range of possible outcomes lower than they were when he was whiffing just once every 10 or 11 swings.

Then comes power.

We’re going to get into some heavy numbers, but it’s important to talk about this specifically. Otherwise, this will be no more than the usual conversation about how, since Mauer hit only four home runs in 2014, his power must be fading.

Here’s a breakdown of all of Mauer’s fly balls and line drives that traveled at least 300 feet, over the past three seasons:

Joe Mauer, 300+ Foot Flies and Liners, 2012-14

(h/t baseballheatmaps.com)

Let’s walk through this. First of all, there’s a clear decline in the number of deep flies and liners Mauer hit in the first place, as a share of his total plate appearances. (A slightly variant form of the same pattern shows up if we take these hits as a percentage of all batted balls: they comprised 12 percent of all his batted balls in 2012, 9.7 percent of them in 2013 and 8.7 percent in 2014. Perhaps, then, Mauer’s power outage began last year, not this one.)

The angle column is telling you where, on average, the batted balls in question went. The left-field line is -45 degrees. Dead center field is 0 degrees. So, in 2014, Mauer’s average deep fly ball or liner went about one-sixth closer to the left-field line than his average ball in the two previous years. This goes back to Mauer’s inability to get around on the ball, and, like that very first tidbit, highlights the fact that more and more of even his hardest-struck balls went out to center and left-center fields—where they simply can’t do as much damage.

The final column is the easiest to read. Mauer lost six feet of average distance, even in this isolated set of flies that has a fixed floor. That’s jarring. There’s no argument against it. Mauer lost a significant amount of pop in 2014.

Of course, Mauer wasn’t himself for a big chunk of the season. The last thing we need to address, before trying to look into Joe Mauer’s future, is the injury history that seems to define him, and especially, the oblique strain that stole a segment of his 2014 season.

Mauer missed five days with back spasms in May, then went down with the oblique problem in early July. I think it’s safe to say he was something less than 100 percent throughout that first half of the season. After his return in mid-August, he was better.

Joe Mauer, Batting Splits by Half, 2014

(h/t baseball-reference.com)

Mauer walked more, struck out less, had a higher BABIP and notched a higher isolated-power number after returning from injury. It was just six or seven weeks, but does that improvement foretell a return to the kind of production a team needs from its regular first baseman?

Not really.

Here’s where pitchers pitched Mauer from the start of the 2007 season through the end of 2013:

Here’s the same chart, for the first half of 2014:

And here’s the same thing, for the second half of 2014:

(BrooksBaseball.net rocks.)

It’s clear that the pitchers Mauer faced over that short span after returning from his injury no longer feared him. They stopped pounding the area just off the outside corner, near the knees, and began attacking him inside. Mauer responded by hitting the ball better, and his power ticked up slightly, but it was still well below the league average—for anyone, let alone for a first baseman. He didn’t punish his opponents for pitching into his wheelhouse; he did more or less what we would have expected him to do with those pitches, even taking his weak first half as a baseline.

Rob Arthur did some marvelous research for Baseball Prospectus this year, demonstrating that pitchers often change the way they pitch a batter before it becomes wholly clear that the batter’s skill level has changed. If that’s true, and if the sample here is sufficient to draw any conclusions (I’m not sure whether it is, in truth, but I think it is), then it follows that Mauer’s power outage is real, not a fluke, and that the rest of the league is aware of the problem.

Let’s Spin This Forward

Is Mauer doomed as a hitter? Surely not. He’s still a sound hitter, in some ways, and if he’s healthier in 2015, he might even get some of the explosion back and rediscover his ability to put a charge in the ball. He’ll continue to post an OBP well above the league average for a while. To meet the offensive standard of a first baseman with aging legs, though, Mauer has to make mechanical and mental changes. He needs to pull the ball in the air more often, and do so with some authority. If he doesn’t, he’ll continue to post solid numbers, but will force the Twins to find a lot of offensive production at positions where it can be in short supply.

Thanks to baseball-reference.com, FanGraphs, brooksbaseball.net, baseballsavant.com, baseballheatmaps.com and Baseball Prospectus for making all of the data used in this post available for free. What a time to be alive.