This was also their last season wearing purple and teal primary uniforms as they made the switch to Sedona red and black in November 2006.
During the 2005 off-season, the Diamondbacks made several key moves to bolster a disappointing pitching staff and improve the team defensively.
Key player acquisitions included catcher Johnny Estrada; right-handed pitchers Orlando "El Duque" Hernández and Luis Vizcaíno; outfielder Chris Young; second baseman Orlando Hudson[2](a Gold Glove Award recipient in 2005 with the Toronto Blue Jays), for whom Troy Glaus was traded; right-handed pitcher Miguel Batista (previously a member of the Diamondbacks from 2001–2003, including the 2001 World Series team); free-agent outfielder Eric Byrnes and veteran free agent pitcher Terry Mulholland (who would go on to spend two separate stints on the disabled list and get released in late June).
1 overall pick in the 2005 First-Year Player Draft, to a $6.1 million contract that included a trip to spring training as a non-roster invitee.
Frustrated by not having a set spot in the rotation, Hernandez was traded to the New York Mets in exchange for reliever Jorge Julio on May 24.
Based on several media reports that appeared on June 7, reliever Jason Grimsley admitted to taking illegal performance-enhancing drugs, specifically human growth hormone, as part of the IRS probe of BALCO, best known for similar allegations concerning San Francisco Giants star Barry Bonds.
The Diamondbacks returned from a 10-game East Coast road trip in which they won 7 and lost 3 (including the above-mentioned 4-game sweep of the Braves) and found themselves 2½ games in front of the Los Angeles Dodgers by June 5.
However, the team entered a freefall immediately following the Grimsley scandal, starting with a lengthy homestand in which they did not won a single contest until their June 13 home win against the Giants.
The bullpen in general, while showing brilliance early on, struggled somewhat as a whole in June, although Julio ended the month with his seventh save in eight chances.
Luis Gonzalez struggled somewhat offensively before the All Star break; it wasn't until June 27 against the Seattle Mariners that "Gonzo" hit his first home run since April 20.
According to reports on Diamondbacks flagship radio station KTAR and in the Arizona Republic, RHP Russ Ortiz, who had a highly disappointing tenure with the D-Backs after signing a $33 million contract during the 2004 offseason, was designated for assignment (DFA) on June 13.
(Ortiz struggled with the Orioles during the remainder of the 2006 season, losing his role as a starter with that organization, but after regaining his form somewhat in winter ball in Puerto Rico, Ortiz was signed by the San Francisco Giants in January 2007 and after a good spring training campaign, was eventually named the Giants' fifth starter for the 2007 season.
Gonzalez reportedly interpreted his benching in a negative manner; he took it as a sign the organization may be ready to part company with him at year's end.
On August 7, the D-Backs acquired RHP Liván Hernández from the Washington Nationals in exchange for minor league pitching prospects Garrett Mock and Matt Chico.
The Diamondbacks flirted with trading for a pitcher before the July 31 trade deadline but made no moves at that time; after All-Star Brandon Webb (the ace of the Diamondback pitching staff and widely considered a candidate for the NL Cy Young Award) missed his scheduled August 5 start against Houston with a sore elbow, it became more urgent to add a starter to the rotation.
He was greeted with standing ovations from the fans, many of whom disapproved of Gonzo's not being part of the future plans of the ballclub (paid attendance was 48,946, the largest regular-season crowd in franchise history).
Despite strong late-season performances from José Valverde, who returned to the closer role in early September as a much improved relief pitcher, finishing the season with 18 saves, as well as other called-up Baby Backs including CF Chris Young and infielder Alberto Callaspo, the Diamondbacks lost 18 games in the month of August, including being swept in three games at San Francisco.
RHP Brandon Webb, a product of the Diamondback farm system, became the ace starting pitcher of the club for 2006 after signing a four-year contract extension.
Trevor Hoffman of the Padres and Chris Carpenter of the St. Louis Cardinals (the eventual 2006 World Series winners) were runners-up in the voting.