Los Angeles Angels Minor leagues Walden was drafted by the
Los Angeles Angels in the 12th round, with the 372nd overall selection, of the
2006 Major League Baseball draft, and began his professional career the next season. Walden pitched for the rookie-level
Orem Owlz in 2007, going 1–1 with a 3.08 ERA in 15 starts. In innings, he allowed 49 hits and three home runs while striking out 63 batters. Prior to the 2008 season,
Baseball America named Walden the 81st best prospect in minor league baseball. He split that season between the Single-A
Cedar Rapids Kernels (with whom he went 4–6 with a 2.18 ERA in 18 starts) and the High-A
Rancho Cucamonga Quakes (5–2, 4.04 ERA in nine starts), going a combined 9–8 with a 2.76 ERA in 27 starts. He pitched 156 innings, allowing 122 hits and seven home runs while striking out 141 batters. Before the 2009 season, Walden was named the 70th best prospect in baseball. He pitched for the Double-A
Arkansas Travelers and went 1–5 with a 5.25 ERA in 13 starts that season. In 2010, he converted to relief pitching, spending 38 games with the Travelers and six games with the Triple-A
Salt Lake City Bees without making a start. Walden also was named
Texas League Mid-season All-Star from the
Arkansas Travelers in 2010.
Major leagues The Los Angeles Angels promoted Walden to the
major league roster on August 22,
2010, by purchasing his contract from
Triple-A Salt Lake. Within the first week of his major league career, Walden's fastball had been recorded at speeds up to . When the Angels traded
Brian Fuentes to the
Minnesota Twins on August 27, 2010, they began to use Walden as their
setup pitcher in his place in the eighth inning. Walden recorded his first MLB
save on September 19, against the
Tampa Bay Rays. The Angels named Walden their full-time
closer on April 5,
2011, replacing
Fernando Rodney. On July 7, Walden was selected to appear in the
MLB All-Star Game for the first time, taking the place of an injured
Mariano Rivera. He recorded his 30th save for the first time on September 13 against the
Oakland Athletics, and finished the season with 32. In 2012, Walden struggled with his command early in the season. The Angels demoted him from the closer role on April 27, replacing him with
Scott Downs.
Atlanta Braves On November 30, 2012, the Angels traded Walden to the
Atlanta Braves in exchange for pitcher
Tommy Hanson. He pitched 47 innings, with a 4–3 win–loss record, 3.45 ERA, and 54 strikeouts during the 2013 season. Walden agreed to a one-year contract for the 2014 season, worth $1.49 million.
St. Louis Cardinals On November 17, 2014, the Braves traded Walden and
Jason Heyward to the
St. Louis Cardinals in exchange for
Shelby Miller and
Tyrell Jenkins. Walden and the Cardinals signed a two-year extension on December 23, 2014, worth $6.6 million. Through April 29,
2015, he made 12 appearances with 12 strikeouts and one run allowed in innings pitched for an 0.87 ERA. However, Walden was unable to pitch after that due to shoulder stiffness. On May 6, he was diagnosed with a right
shoulder strain. The Cardinals initially estimated a timetable of six-to-ten weeks before he could return to pitching, but recovery took much longer than expected. Instead, Walden's shoulder did not recover, leaving the possibility of surgery to repair the
rotator cuff. On September 6, the Cardinals ruled out his return for the remainder of the season. Walden rehabilitated the shoulder the following off-season in the
Dallas–Fort Worth metroplex, adopting a program that was five days a week, four hours per day. He worked with former teammate
Matt Belisle. After sustaining a grade 2
latissimus dorsi muscle strain, the Cardinals placed Walden back on the disabled list to start the
2016 season. He became a free agent following the season. On November 12, 2016, Walden signed a minor league contract with the
Atlanta Braves. The Braves and Walden mutually agreed to void his contract on February 9, 2017, after discovering that his rehab had not been progressing as expected. ==Pitching style==