Does defense matter in fantasy baseball? While it doesn't factor directly in scoring, it does matter where your players appear in the field. Players start the season with position eligibility based on the prior season. Players that switch positions have to play a minimum number of games before they meet their league requirements for eligibility at the new position. There are two time lags: one in retaining legacy positions and another in qualifying for new positions.
Switching from the outfield to a middle infield position can greatly enhance fantasy value. Middling production from an outfielder equates to above average production at second base, for example. Players that recently gained eligibility as a middle infielder or catcher or that are on the cusp of doing so are for better.
Position changes are not necessarily beneficial, however. There are a number of position players that are effectively trading down. They are moving from shallow fantasy positions to deeper fantasy positions. They will keep that legacy position for the remainder of 2009 but lose it next season. Enjoy the eligibility while you can since their long-term values will reduce (for worse).
Pablo Sandoval, 3B/1B/C, Giants: As a late-season call-up in 2008, Sandoval played 17 games at first, 12 at third and 11 at catcher. Sandoval is eligible at all three spots in some formats, such as Yahoo!, but in other systems he has only corner infielder ratings. The catching rating is gold in fantasy. Though playing exclusively at third base this April, Sandoval could eventually make a few appearances behind the plate giving Bengie Molina a day off. That would give him the magic "C" next to his name in leagues where Sandoval doesn't already have it. Don't fret about Sandoval's slow start, hitting only .192 -- he will hit. He hit .345 in 145 at bats in 2008 and was a lifetime .308 hitter in the minors. Sandoval will hit well above the average catcher and is a valuable fantasy commodity at the thinnest position.
Skip Schumaker, OF/2B, Cardinals: Tony La Russa's bold experiment is moving an excess outfielder, Schumaker, to a new position. Schumaker had little value as a fantasy outfielder since he lacked power. However, as a .300 hitting second baseman with a lot of runs scored his value skyrockets.
Mark Teahen, 1B/3B/OF/2B, Royals: Teahen was primarily an outfielder in 2008 (119 games) with another 19 appearances at third base and 14 at first base. This season he has appeared in three games at second base and will play there a lot more goring forward. Teahen (.292) will gain eligibility at 2B in all leagues within the next two weeks. At that point he will be worth a look as a possible waiver pickup. Teahan has hit as many as 18 HR in a season (2006) and has had as many as 13 steals (2007) in a season.
Emilio Bonifacio, 2B/3B, Marlins: Bonifacio is off to one of the all-time great starts. His .500 average is second in the NL and he leads in runs and stolen bases. A position change, from second base to third, gives him dual eligibility and added flexibility to your fantasy lineups. In some leagues he has not earned the 3B rating yet, but that will come later this week. Technically, this is trading down, but Bonifacio was not on the fantasy radar as a second baseman last year, so therefore no value is lost.
Michael Young, 3B/SS, Rangers: Young has been one of the better fantasy shortstops since 2003. This season he moved to third base to accommodate rookie Elvis Andrus and very soon Young will have dual eligibility at shortstop and third base. That's good for now, but long term the position switch devastates Young's fantasy value. In 2010 he will strictly be a third baseman and he will not compare as closely to Alex Rodriguez as he does to Derek Jeter.
Chone Figgins, 3B/2B, Angels: Figgins was eligible at three positions two fantasy seasons ago. Then he lost the OF rating last year and stands to lose the 2B rating next year. Figgins is a great source of stolen bases, but he would be much more valuable as a middle infielder. He is exclusively a third baseman now.
Aubrey Huff, 1B/3B, Orioles: Huff was one of the big surprises of 2008, hitting .304 with 32 HR while splitting time between 1B and 3B. This season he has only played first base. Ty Wigginton will be Melvin Mora's caddy, not Huff, so say goodbye to that 3B rating next year.
Mark DeRosa, 2B/3B/OF, Indians: Include me with the skeptics as far as DeRosa is concerned. He hit 21 HR for the Cubs last season, about double what you would have expected based on past history. His production was great and he did it at 2B, 3B and OF. As a Cleveland Indian, he is playing only third base. DeRosa, as a straight third baseman, is worth a lot less. Did I mention he is hitting .115?
Carlos Guillen, 3B/1B/OF, Tigers: Guillen had shortstop eligibility last season. Depending on your league, this year he is some combination of third base, first base and outfield. As Guillen's skills decline he has moved to less desirable fantasy positions. That's a bad combination. Next year, as a straight outfielder, he will be unplayable in fantasy.
Alexei Ramirez, 2B/SS/OF, White Sox: Short term, Ramirez (.160) is a train wreck. Long term, he loses the SS and OF ratings as soon as next season