Injuries took their toll on Twins catcher Joe Mauer last year. So did Target Field.

Understand this: He loves the new ballpark. The St. Paul native knows as well as anybody what it means to the franchise. He's quick to note that the Twins posted the American League's best home record, 53-28, in their first year in their gorgeous new facility.

But on an individual level, Target Field wasn't kind to Mauer. Leaving the Metrodome made it harder for him to prove his worth, especially after signing his eight-year, $184 million contract extension.

Twins fans were euphoric when he signed that deal, one year ago Monday. But by season's end, it was fair to ask if the Twins overpaid.

After hitting 28 home runs in his 2009 MVP season, Mauer hit nine homers last season, including one at Target Field.

"A lot of times, I was hitting balls to left field that would be out of a lot of other parks, and they were caught for outs," Mauer said. "So you try to muscle it up a little bit more, and you become a little late [with each swing]. So yeah, it definitely does play with your mind."

According to's Park Factors, Target Field was the toughest home run park in the majors. As a team, the Twins hit 52 homers at home and 90 on the road, and their pitchers allowed 64 homers at home, compared to 91 on the road.

Besides adjusting to his new home ballpark, Mauer was beat up most of the season. On April 30, he jammed his left heel on first base and suffered a deep tissue bruise. At the All-Star break, he needed a cortisone shot to relieve pain in his right shoulder.

At the break, Mauer was batting .293 with a .368 on-base percentage and .424 slugging percentage. But then it was almost like he flicked a switch. After the break, those numbers improved to .373, .447 and .527.

"What I was proud of last year was making the adjustment, and it ended up being a pretty good year," said Mauer, who finished third in the AL batting race, at .327.

What adjustment did he make?

"I kind of almost got over the fact I'm probably not going to hit too many homers at home," he said. "Just keep it simple, try to hit hard line drives, find those gaps and run a little bit."

Mauer finished with 43 doubles, up from 30 in his MVP season, but his RBI total dropped from 96 to 75. After he raised the bar so high in 2009, his season was widely viewed as a disappointment.

The Twins will be paying him $23 million for the next eight years. For that, they might expect more home runs.

"The contract wasn't done in a one-year vacuum," Twins General Manager Bill Smith said. "It's the body of work that Joe had from 2005 through 2009. And we look forward to the coming years, hopefully the coming decade, with Joe Mauer as one of the cornerstone players in this franchise."

Leap of faith

The Twins alleviated many fears last March 21 when they gave Mauer his contract extension. He was entering the final year of his previous deal and could have become a free agent after the season.

It was not unlike the LeBron James situation in Cleveland, as a franchise faced the prospect of losing a star player with deep local ties. This spring, Albert Pujols is in his final year before free agency, and he broke off talks with the Cardinals after they reportedly offered him about $200 million, well below the 10-year, $275 million deal Alex Rodriguez has with the Yankees.

Like Pujols, Mauer made it clear that he did not want his contract talks going into the season. Mauer's agent, Ron Shapiro, called it a "textbook" negotiation.

"The club may have wanted fewer years, and we may have wanted the right to walk away if the market changed radically," Shapiro said. "I think we traded those so we could get to a solution. I think the end result was that neither Joe nor Minnesota had to go through, really, the torture that both Pujols and St. Louis have gone through this spring."

Now the stakes are higher. Mauer, who turns 27 on April 19, made $12.5 million last year, so his salary has almost doubled again.

The Twins would have risked losing Mauer had they let him reach free agency, a prospect nobody in Minnesota wanted to think about last year.

But based on his 2010 season, his earning power wouldn't have been as high. Not only was he less productive offensively, but new durability concerns were raised. In mid-December he underwent arthroscopic left knee surgery for the second time in seven years.

Tim Dierkes, who studies the free-agent market closely at, said he believes the Red Sox, Rangers and Angels would have joined the Twins in pursuit of Mauer, with Boston making the strongest push.

Dierkes estimates Mauer would have commanded a deal comparable to the rumored deal the Red Sox are considering for Adrian Gonzalez -- seven years for $154 million -- so maybe the Twins could have saved $30 million by rolling the dice.

But last March, they risked seeing Mauer duplicate his 2009 success before hitting the market. Dierkes said this might have pushed Mauer's next contract into the eight-year, $200 million range.

Either way, Smith said, "We're thrilled with the way the negotiations went, and we're happy with the final result."

Twenty percent rule

After signing Mauer, Twins CEO Jim Pohlad promised the team's payroll would increase.

This answered an important question because in recent history, only one team has won the World Series with one player making more than 20 percent of the team's payroll -- the 2003 Marlins with catcher Ivan Rodriguez.

This so-called 20 percent rule suggests that with Mauer at $23 million, the Twins had to increase their payroll to at least $115 million. They are projected to open the season at about $113 million, which doesn't include the $5 million posting fee they paid the Chiba Lotte Marines for Japanese infielder Tsuyoshi Nishioka.

The Twins spent about $101 million on payroll last season.

"One of the things they assured us when they signed me is that we're going to be able to field a good team," Mauer said. "I told them that's one of my goals: I want to win. That's why I signed. I was convinced, and I still am, that we can win here."

Of course, having Mauer on the field makes a big difference. Even though he didn't go on the disabled list last year, he had 22 fewer plate appearances than he had in 2009, when he missed all of April because of a lower-back injury.

He has spent the spring trying to rebuild leg strength from the knee surgery and didn't catch in his first Grapefruit League game until Saturday, when he went 1-for-2 with a walk and an RBI. After catching five innings, Mauer said he felt good but hinted he might need more noncatching days in April, as the Twins have just one open date over the season's first 24 days.

Eventually, the Twins and Mauer might have to seriously contemplate a position change, but the team is convinced it made the right decision when it gave Mauer his contract extension.

Maybe other teams have struggled with one player taking up a high percentage of the team's payroll, but as Smith said last March, "I'm not sure many teams have had a player like Joe Mauer."