Much has been made of Twins fans booing Joe Mauer at Target Field this year. Personally, I'm not offended by it. It's how some invested fans choose to express their disappointment and frustration. They paid for the tickets that help pay the players' enormous salaries, so those in attendance should be free to voice their displeasure with what's happening. In this case, it's not totally unjustified.

Not that I myself would ever boo Mauer. There have been ball players in this game's long history who have been deserving of booing – scumbags, entitled pricks and racists among them – but No. 7 is not (at least to my knowledge) any of those things.

He's a very handsomely paid athlete who is not currently providing the value that the Twins hoped for and expected when they inked him to a $184 million contract extension three years ago. I doubt it's his fault.

It's not like Mauer isn't trying, which is why the booing strikes me as odd. By all accounts, he worked out like a maniac during the offseason, desperate to distance himself from the nightmare season that was 2011. But I do wonder if it's a little too late, and the years of punishment behind the plate have fundamentally weakened him as a hitter.

After grounding out three times on Wednesday, Mauer is now hitting .270/.391/.365 on the campaign. That's far from embarrassing, but it's also quite similar to the .287/.360/.368 line he finished with last year, when he admitted he never felt right all season. Last year Mauer totaled three home runs and 15 doubles in 333 plate appearances. This year, at his current pace, he'll have 16 doubles and two homers when he reaches that PA mark. That's a real lack of power, and it stems from an increasingly extreme ground ball rate.

His approach at the plate has been excellent. He's striking out at a measly 9.3 percent clip (ninth-lowest in the majors) and he's on pace to draw more than 100 walks. Yet when he puts the ball in play, he rarely does so with authority. His 58.7 percent grounder rate eclipses last year's 55.4, which was at the time a career high.

He's still a great, professional hitter, but when I see him now I just don't see signs of the the dominant player who in 2009 hit .365 with 28 homers. I don't even see the guy who in 2010 hit .327 with 43 doubles. It was some hybrid of those models that the Twins hoped they'd be getting at least in the early years of his contract, but right now Mauer appears headed toward rather quickly becoming a first baseman and No. 2 hitter who takes great at-bats and gets on base a ton but doesn't hit for much power or run well.

That's not a $23 million franchise centerpiece. It's Doug Mientkiewicz. And that's why the people boo.

But Mauer is out there on the field every day, trying to get things figured out, so you won't hear me joining the chorus. Catching for many years takes a toll, even on the most pristine of athletes. I wrote an article last year framed around one of my favorite quotes from Johnny Bench: "A catcher and his body are like an outlaw and his horse. He's got to ride that nag till it drops."

Bench was one of many backstops who have either retired early, switched positions or seen their production wane rapidly with age. I'll name another example – one with parallels to Mauer that cannot be ignored: Jason Kendall.

Kendall spent the first nine years of his career in Pittsburgh, serving as a full-time catcher and hitting .306/.387/.418 while averaging eight home runs. In 2005, at age 30, he was traded to the Oakland A's, and over the next six years he would hit .260/.333/.318 while hitting eight home runs total.

Kendall retired at age 36, which will be Mauer's age when his contract with the Twins is up.