There's a very energetic discussion going on about whether Joe Mauer is on track to get into the Hall of Fame after he retires, and in the spirit of maintaining that discussion, I've put together what I think is a reasoned set of answers to Bill James's famous 'Keltner list' questions regarding Joe Mauer's career so far. Keep in mind that the Keltner list isn't intended to answer all questions about a player's Hall credentials, but rather to serve as a checklist to make sure you're looking at lots of different pieces of evidence rather than focusing on only the stuff that supports the conclusion you want to reach.
So without further ado:
Was he ever regarded as the best player in baseball? Did anybody, while he was active, ever suggest that he was the best player in baseball?
Yes, there have been folks who have suggested that Mauer was the best player in baseball. More about this later.
Was he the best player on his team?
Despite Justin Morneau winning the MVP award in 2006, it's likely that Mauer has been the best player on the Twins every season since Johan Santana was traded to the Mets.
Was he the best player in baseball at his position? Was he the best player in the league at his position?
The intriguing thing about Mauer's reign as 'best catcher in baseball/in the AL' is that it's largely been retroactive -- when Mauer was winning the MVP by consensus in 2009, many writers liked to point out that Mauer probably should have won the MVP in 2006, and had likely been the best catcher in baseball/in the league from that time. Some of that momentum was lost in 2010 as the Twins were again swept out of the post-season by the Yankees, and the talk has all but dried up after Mauer's injury-riddled 2011 season in which the Twins fell from pennant contenders to AL Central cellar-dwellers.
Unlike players like Willie Mays and Albert Pujols, Mauer's 'reign' as best catcher in baseball/the AL appears to have largely passed by before many folks outside Minnesota really noticed. And it should be pointed out that Mauer no longer comfortably owns either the 'best catcher in baseball' or 'best catcher in the AL' titles, based on this list from elsewhere on SB Nation.
Did he have an impact on a number of pennant races?
Though Mauer played very little during the Twins successful AL Central run of 2004, Mauer was integral to the Twins division runs in 2006, 2008, 2009, and 2010, three of which were successful. It would be hard to claim that his performance didn't have a positive impact.
Mauer's injuries were given as one reason why the Twins collapsed from pennant-contenders to nearly 100 losses in 2011, but given that Mauer resurged to at least his old offensive form in 2012 but the Twins barely improved as a ballclub, it's reasonable to question that correlation.
Was he a good enough player that he could continue to play regularly after passing his prime?
We'll know this better by the time Mauer's contract expires, though a decent leading indicator will be if Mauer is both still catching and still contending for a batting title in 2014, at the age most catchers are seeing their performance begin to degrade.
Is he the very best player in baseball history who is not in the Hall of Fame?
Hard to say at the moment, even harder to predict given who might or might not be in the Hall by the time Mauer is eligible. I'd have to put him behind Albert Pujols at least, though.
Are most players who have comparable career statistics in the Hall of Fame?
If Mauer retired with his current career statistics, the answer would almost certainly be 'no'; none of Mauer's career comps is a Hall of Famer and only a couple would likely even have Hall cases (Victor Martinez and Hanley Ramirez, specifically). However, when looking at comps by age, Mauer's chances look a lot better - five of Mauer's top ten age 29 comps are Hall members (Michey Cochrane, Travis Jackson, Bill Dickey, Charlie Gehringer, and Lou Boudreau) and two more are almost certainly going to be Hall members eventually (Derek Jeter, Craig Biggio). Note, though, that projecting a Hall berth for Mauer based on his of-age comps presumes that he will age similarly to most of his comps -- otherwise he could find himself with a career much more comparable to his of-age comps Jason Kendall (for whom age and a move to a pitcher-friendly ballpark at age 31 led to a decline in his numbers) or Jose Vidro (who seriously declined as an age 33 player and was out of baseball following that season).
Do the player's numbers meet Hall of Fame standards?
Based on the baseballreference.com measure, Mauer meets 45% of the Hall's standards, where the average Hall member meets 50%.
Is there any evidence to suggest that the player was significantly better or worse than is suggested by his statistics?
In Mauer's case, it's almost the converse. Mauer has a much better reputation as a player than his numbers would generally suggest.
For instance, Mauer has the reputation for being an outstanding defensive catcher. Yet advanced defensive metrics show that Mauer, for his career, has been a net 11 runs below average as a defensive catcher over his 9 seasons with the Twins and has never been better at preventing runs than he was in the 257 innings he played as a rookie in 2004. Similarly, though Mauer led all catchers by throwing out 53% of would-be basestealers in 2007, Mauer's performance in that stat since 2009 has been poor enough so that his overall success rate throwing out basestealers hasn't been that much above the league average (32% caught in Mauer's career vs 27% caught league-wide over the same years). It is perhaps no coincidence that Matt Wieters, not Mauer, has won the AL Gold Glove each of the past two seasons.
Likewise, Mauer's reputation as a hitter is based largely on his three batting titles, something no other AL catcher has done even once. Yet other than his MVP season of 2009 where he combined his league-leading .365 average with 28 home runs, Mauer's slugging percentage has been poor for a player who bats consistently in the #3 slot of his team's batting order. It should be noted as well that among Mauer's of-age comps in or likely to be in the Hall, most are middle infielders, not catchers -- and the great-hitting Hall catchers like Bench, Carter, and Berra don't appear on Mauer's comp list at all. This also suggests that Mauer's best shot at maintaining a Hall of Fame career is to move to the infield as Craig Biggio did.
Is he the best player at his position who is eligible for the Hall of Fame but not in?
At the moment, no -- that would be Ivan Rodriguez, who is also still active. Assuming Rodriguez gets in before Mauer is eligible, and that Piazza either gets in or is unofficially disqualified due to steroid rumors, Mauer would likely qualify -- he is already ahead of Jorge Posada by JAWS -- unless one of the young catchers currently coming up behind him (*cough* Buster Posey *cough*) surpasses him.
How many MVP-type seasons did he have? Did he ever win an MVP award? If not, how many times was he close?
If one measures MVP-type seasons as being of 8 WAR or higher, then Mauer has had none, though his 2009 season is probably close enough to count (7.6), since he actually won the MVP award that year. Some observers, including writer Joe Posnanski, have asserted that Mauer, not Justin Morneau, was actually the most valuable Twin in 2006 and should have won the award then as well.
Mauer has finished in the top ten in MVP voting 4 times in his 9 year career, which is a very good showing.
How many All-Star-type seasons did he have? How many All-Star games did he play in? Did most of the other players who played in this many go to the Hall of Fame?
If an All-Star type season is defined as roughly 5+ WAR, then Mauer has had 5, including his MVP season. He has played in five All-Star games, starting three at catcher. That's a good total given his 9 year career, though Mauer would need to continue to be elected or named to later teams to bolster his total -- five total All-Star appearances would be a low number for a Hall of Famer of the All-Star era.
If this man were the best player on his team, would it be likely that the team could win the pennant?
It seems pretty clear that a team with Mauer as its best player could win a pennant, though none of Mauer's Twins teams has done so yet.
What impact did the player have on baseball history? Was he responsible for any rule changes? Did he introduce any new equipment? Did he change the game in any way?
When Mauer was first making a splash in the major leagues, some attention was given to the 'Quickswing' device that Mauer's father invented for him and that was given some credit for developing Mauer's fast batting reflexes. It's not clear that the 'Quickswing' has survived the test of time, however.
Did the player uphold the standards of sportsmanship and character that the Hall of Fame, in its written guidelines, instructs us to consider?
To the best of anybody's knowledge, Mauer has done this consistently in his career.
My conclusion, which I mentioned in the comments of the thread linked at the top of the page, is that the reasonableness of Mauer's Hall case depends on how he finishes the 2014 season. If he's still catching regularly and still contending for batting titles, his chances look much better than if he suffers another serious injury and/or begins entering the decline phase of his career early (which high-average/low-power hitters have a tendency to do).