Minor league roster moves occur often and sometimes mysteriously. Seemingly healthy players go on the disabled list, others are sent to teams that are not playing, and others work out as orphans in Florida.

Players who appear healthy suddenly come up with minor injuries – strained calf is a favorite ailment. Sea Dogs infielder Zach Borowiak played nine innings of a spring-training game and then was put on the DL when the season started.

Other players get transferred to the Lowell Spinners. They don't actually drive down to LeLacheur Park, since no one is there: The Spinners' season does not start until June.

Pitcher Blake Maxwell was "sent" to Lowell briefly last week to make room for Borowiak on the active roster.

Then there is extended spring training in Fort Myers, Fla., the limbo for players with no place to call home. Some players are recovering from injuries, like Sea Dogs catcher Jon Otness.

All the moves are done in the name of depth. For all kinds of reasons, especially legitimate injuries, teams need extra players. And they do not just come out of thin air – or cornfields, for you "Field of Dreams" fans.

Before the Red Sox built their minor league development machine, they used to be in a mad scramble to fill roster spots, plucking players from waiver wires and independent leagues.

Players, mostly unknowns, came and went with regularity. I still remember an outfielder introducing himself to Sea Dogs Manager Ron Johnson on the day before the 2003 season began, and Johnson had no idea who he was.

THE RED SOX depth in the minor leagues was noticeable in spring training, with a total of 27 infielders and outfielders (a 28th was signed later).

There were 11 infielders: Nick Green, Gil Velazquez, Angel Chavez, Ivan Ochoa, Jeff Natale, Iggy Suarez, Borowiak, Argenis Diaz, Jorge Jimenez, Ryan Khoury and Lars Anderson (the Red Sox later signed a 12th, Travis Denker).

There were five others that could play the outfield or first base: Brad Wilkerson, Jeff Bailey, Chris Carter, Paul McAnulty and Aaron Bates. And there were two who could catch and play first base: Sandy Madera and Jon Still.

Then there were nine outfielders: Zach Daeges, Jeff Corsaletti, Chip Ambres, Jon Van Every, Sean Danielson, Josh Reddick, Bubba Bell, Reid Engel and Daniel Nava.

What to do with 27 players for 18 spots, 20 counting the DH for both Triple-A Pawtucket and Double-A Portland?

Green and Velazquez are in Boston, replacing the injured Julio Lugo and Jed Lowrie.

Carter was in Boston, replacing the injured Mark Kotsay. Bailey was called up to replace the injured Rocco Baldelli, and then Van Every was summoned to replace Carter.

In Pawtucket, Wilkerson retired. McAnulty and Carter play first or DH. The rest of the infield has Chavez, Ochoa, Denker, Lugo (on a rehab assignment) and Suarez (just called up from Portland, replacing the injured Natale). Madera is on the DL.

Corsaletti, Danielson and Ambres play the outfield. Daeges is hurt.

In Portland, the infield is set with Anderson, Khoury, Diaz and Jimenez, with Borowiak as the backup. Still is the DH and a backup at first base. Bates, Reddick and Bell play the outfield, with Engel as the backup.

Nava, 26, who hit .342 in advanced Class A last year, played with the Sea Dogs in spring training, but he hurt his leg and was sent from Double-A to the advanced Class A roster and is still on the DL.

More movement is coming. Lugo is expected back Monday, and Kotsay could return soon after.

The revolving rosters may make you dizzy, but ultimately that's what keeps the Red Sox machine moving.

PITCHING DEPTH also is evident in the Red Sox organization.

When Daisuke Matsuzaka went down with a sore shoulder, the Red Sox had options. They decided to move Justin Masterson back to the rotation...