Updated

The Houston Astros selected right-handed reliever Josh Fields from the Boston Red Sox organization with the first pick in Major League Baseball's annual Rule 5 Draft on Thursday.

Fields, a first-round pick by the Seattle Mariners in the first-year player draft back in 2008, pitched to a 2.01 ERA across 58 1/3 innings at both Double- and Triple-A this past season in the Boston system.

The 27-year-old had struggled with his command early in his career, but only walked 18 batters a year ago. Quite a contrast from the 5.9, 5.7, and 6.7 batters he walked per nine innings in his first three pro seasons.

In 10 games for Triple-A Pawtucket, Fields was 1-0 with four saves and struck out 19 without walking a batter over 13 2/3 innings.

Boston got Fields in the Erik Bedard trade and chose not to protect him. He now must stay on Houston's 25-man roster for the entire season or be offered back to the Red Sox for $25,000, half the price they will receive from the Astros for taking him.

However, Houston may at any time waive Fields and if he does not sign with a new team, he must be offered back to the Red Sox, effectively canceling the Rule 5 draft choice.

Once he spends an entire season on his new team's 25-man roster, though, Fields' status reverts to normal and he may be optioned or designated for assignment.

Those same rules apply to all 13 players who were taken in the major league phase of the draft on Thursday.

Several players have succeeded through the Rule 5 Draft in the past, most notably Hall of Famer Roberto Clemente, two-time Cy Young Award winner Johan Santana and 2010 AL MVP Josh Hamilton. Other prominent players selected through the Rule 5 Draft include pitchers Joakim Soria, Matt Mantei and Antonio Alfonseca, as well as second baseman Dan Uggla and outfielders George Bell, Willy Taveras and Shane Victorino.

Players who are not currently on their team's 40-man roster are eligible to be taken in this draft, but only after a standard exemption period has elapsed. Also, only teams whose rosters are under the 40-man limit are eligible to participate.

A player who is 18 when he's signed can spend five seasons in an organization before he has to be protected. Anyone who is 19 or older must be protected after four years. Once past that time of service, a player must be put on the 40-man roster if that team wants to keep him from becoming eligible for the Rule 5 Draft.