On May 1st, 2009, Joe Mauer stepped into the Metrodome batter’s box against Kansas City righty Sidney Ponson. Mauer, making his season debut after missing April with a lower back injury, worked a 2-0 count and then smacked a Sir Sidney fastball over the left field wall. The drive set the tone for a season in which the lefty batter, known for lacing line drives, showed unprecedented power.
Mauer, of course, was already among the better hitters in the game. The three previous seasons, he posted a .378 wOBA and a 134 wRC+. But in 2009, Mauer mashed to the tune of a .438 wOBA and a 174 wRC+. Among qualified big league hitters, Mauer’s wOBA placed behind only that Pujols fellow in St. Louis.
The main reason for the offensive uptick was a dramatic increase in Mauer Power. From 2006 to 2008, the first overall pick in the ’01 draft had a .138 Isolated Power. In 2009, Mauer’s ISO spiked to .222. After, as Carson Cistulli would say, jacking a donger on 8.1 percent of his fly balls hit the preceding three years, Mauer hit a round-tripper 20.4 percent of the time that he lofted the ball in 2009.
Heading into 2010, many wondered how much of that extra power Mauer would retain. It would be rash to just expect him to lash extra-base hits and homers at the same rate as in ’09 from now on. At the same time, expecting total regression back to that previous .130-.140 ISO area would be to ignore a power display that holds statistical significance. CHONE projected a .401 wOBA and .178 ISO from Mauer in 2010, while ZiPS had a .415 wOBA and a .189 ISO. The FANS forecast called for a .409 wOBA and a .200 ISO.
So far, Mauer has a .351 wOBA and a 119 wRC+ in 286 plate appearances. Part of that lower-than-expected wOBA can be explained by a .321 BABIP that’s 21 points below his career average, but Mauer’s pop has reverted to his pre-’09 level, and even a bit below it. His ISO is .128, and his HR/FB rate is 4.6 percent.
As Dave Cameron noted over the winter, Mauer has long been a prodigious opposite field hitter. While most batters perform worst when putting the ball in play to the opposite field, hitting lots of weak fly balls and posting mild power numbers, Mauer thrives when he goes the other way. Last season, Mauer’s splits to left field were the stuff of legends:
The above chart is not a typo — Mauer owned a .600 wOBA when hitting to the opposite field, with a .401 ISO. He crushed 16 home runs to left field. This season, Mauer is still a beast when going the opposite way. But his numbers more closely resemble those from 2006 to 2008. He has connected on one home run to left field thus far:
When hitting to center field, Mauer also showed more power than usual and had a higher BABIP in 2009. This season, his ISO and BABIP have come back down:
The 27-year-old has never been a standout hitter when putting the ball in play to the pull side. Most batters post their best numbers when pulling the ball, but Mauer chops the ball into the ground than most — his ground ball rates to the pull side have usually been in the high-seventies, while the average lefty batter hits a grounder when pulling the ball about 59 percent.
In 2010, Mauer has performed even worse than usual when pulling the ball. A low BABIP hasn’t helped, but neither has a sub-.100 ISO. He has yet to go deep when pulling the ball:
On a positive note, considering his backward spray splits, Mauer is pulling the ball less this season — 25.4 percent, compared to 29.3% from 2006-2008 and 32.9% last season.
What should we make of Mauer’s power? I’m not sure, and it’s probably too early to say what effect Target Field has on these figures. My best guess is that he’ll post power numbers somewhere between his ’09 outburst and his current level. Mauer’s rest-of-season ZiPS projects a .164 ISO, and CHONE’s updated projection for June to the end of 2010 had a .174 ISO. Whether he starts hitting the ball more forcefully or merely keeps drawing walks and cracking doubles, Mauer remains one of the most valuable players in the game.
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