According to Joe Posnanski, the Royals are considering moving Mark Teahen to second base.  As he mentions, this makes some sense considering Alex Gordon is firmly entrenched as the third baseman, and the Royals have a glut of corner outfield / first base / DH types (plus Teahen's bat doesn't really play at those positions).

Could this work? After all, Teahen was originally called up as a third baseman in 2005 and stayed there the next season.  In 2007 he was moved from 3B to right field to make room for the aforementioned Gordon, the Royals' top prospect at the time.

From Tango's work on positional values, we know second base and third base have equivalent fielding value.  While that means on average a player who moves between second and third will perform similarly at each position, it's not a given that any individual player will.

What does this mean for Teahen?  Well, the first problem is he wasn't that good a third baseman to begin with.  According to bUZR, Teahen was -17 runs in 2005 and basically average (.3 runs) in 2006.  Since it's been two seasons since he played much infield (he did play about 30 games at 3B or 1B last year), we might assume him to be closer to the 2005 number than to the 2006 number.  In fact, the CHONE projections have Teahen at -11 for third base.

Is there any reason to assume that Teahen's transition will differ from Tango's findings?  I'm not aware whether Teahen has played any second base in the past, but if not, there's likely a need to gain some familiarity with the position, especially making the pivot on the double play.  So it's probably fair to assume his performance at second base would initially be lower than at third base while he adjusts.

What about longer term?  Is there anything specific about Teahen or his skill set that could substantially aid or hamper the change?  His height is a concern.  In the original KC Star article Posnanski references, Sam Mellinger reports there's only been 4 second basemen who stand 6'3" or taller to get 500 plate appearance.  Of course that's an arbitrary cutoff, but it does speak to some perceived impediment of being tall at second base.

Also consider the skills needed at third versus second.  The initial reaction at third base is more important than at second because the 3B is much closer to the batter.  Also, the throws from third base are longer, so arm is generally considered more important there (although second basemen make a higher percentage of their throws moving away from first base, so the arm needs might be closer than one might think).  Looking back at the Fans' Scouting Reports from when Teahen was a third basemen, we find that the fans are concerned with his hands - which should impact either position.  Teahen's a tough player to gauge in the Scouting Report.  His 2005 season rates much higher than his 2006 season - exactly the opposite of what we found looking at bUZR.  2005's ratings suggested Teahen would be a quality third baseman - good first step, strong arm.  His 2006 ratings suggest he should probably put down his glove and become a DH.  So while overall, this look was a little inconclusive, we don't see anything obvious that indicates he'll be better at second than he was at third.

Second base is probably Teahen's last chance as a starter in KC, and I don't necessarily see teams lining up to deal for a mediocre fielding positionless player who's been below average with the bat the last two years.  And that's really the issue.  Despite showing flashes of greatness in the minors and in a somewhat abbreviated 2006 season, Mark Teahen hasn't been that good.  Perhaps the Royals are hoping a return to the infield helps his bat, or they're just trying to see if they can salvage something from him at a position where they don't have many other alternatives.  Either way, it's a risk worth taking, but I'm not so optimistic about it's chance of success.