Middlebrooks was an athletic defensive player and hit for
power and his baserunning was rated as average.
Boston Red Sox Minor leagues Middlebrooks had been projected as a first round talent in the
2007 Major League Baseball draft. However, the belief that he would follow through with his scholarship to Texas A&M led Middlebrooks to fall in the draft. He received a $925,000
signing bonus to renege on his commitment to Texas A&M. He was promoted to the
Salem Red Sox of the
Class A-Advanced Carolina League in 2010 and responded by batting .276 with 12 home runs and 70 RBIs. Middlebrooks also participated in the 2011
All-Star Futures Game, Through August 2011, Middlebrooks batted .306 with 18 home runs and 80 RBIs for Portland, at which point he was promoted to the
Pawtucket Red Sox of the
Class AAA International League. Joe McDonald of
ESPN.com called Middlebrooks "Boston's likely [third baseman] of the future" upon his promotion from Portland to Pawtucket. He hit .161 in 16 games with Pawtucket to close out the 2011 season. After the 2011 season, the Red Sox assigned Middlebrooks to the
Arizona Fall League, where he hit four home runs in 13 games and was named to the Rising Stars Game. In November 2011, Middlebrooks,
Che-Hsuan Lin, and
Drake Britton were added to the Red Sox 40-man roster to protect them from being selected in the Rule 5 draft. Heading into the 2012 season,
Baseball America rated Middlebrooks as the Red Sox' best prospect and 51st best prospect overall. Starting the 2012 season with Pawtucket, Middlebrooks hit .333 with nine home runs and 27 RBIs in 24 games and 93
at-bats.
2012 season The Red Sox promoted Middlebrooks to the major leagues on May 2, 2012, when Youkilis was placed on the
disabled list. He made his MLB debut that day, drawing a
walk in his first plate appearance and recording two hits. On May 6, he hit a game-tying grand slam for his first major league home run in what was eventually a 17-inning loss to the
Baltimore Orioles. In his first 41 games with the Red Sox, Middlebrooks batted .326 with nine home runs and 34 RBIs, the most RBIs to start a career for a member of the Red Sox since
Walt Dropo recorded 37 RBIs in his first 41 career games dating back to 1949–50. Middlebrooks was named
American League Player of the Week for the week ending June 24. Middlebrooks broke a bone in his right hand when he was hit by a pitch in a game against the
Cleveland Indians on August 10, ending his rookie season with a .288 batting average, 15 home runs and 54 RBIs in 75 games played.
2013 season in 2014 On April 7, 2013, Middlebrooks hit three home runs in a 13–0 Red Sox victory over the
Toronto Blue Jays in Toronto. Two of his home runs were hit off pitcher
R. A. Dickey. However, he lost playing time to
José Iglesias after he strained his back in May. After he batted .192 on the season, the Red Sox optioned Middlebrooks to Pawtucket on June 25, 2013. The Red Sox opted not to promote Middlebrooks when they traded Iglesias on July 30, using
Brandon Snyder and
Brock Holt instead. After Middlebrooks made adjustments, the Red Sox recalled him from Pawtucket on August 10. In Game 3 of the
2013 World Series, Middlebrooks was ruled to have obstructed future teammate
Allen Craig after diving for an errant throw at third base. The play awarded Craig the game winning run for the Cardinals. The Red Sox won the series over the Cardinals.
2014 season In 2014, Middlebrooks missed 19 games in April due to a strained calf. In May, he broke a finger, and again went on the disabled list. He had been struggling at the plate to begin the season hitting just .197 with two home runs in 21 games. As he rehabilitated his injury in the minor leagues, Middlebrooks began playing in the
outfield, due to the Red Sox' signing of
Stephen Drew. After the Red Sox traded Drew, they hoped that Middlebrooks would improve his performance with more regular playing time. Middlebrooks continued to miss time later in the season due to lingering effects of the hand injury. He finished the 2014 season with a .191 average in 215 at-bats.
San Diego Padres During the 2014–15 offseason, the Red Sox signed
free agent Pablo Sandoval, a third baseman. On December 19, 2014, the Red Sox traded Middlebrooks to the
San Diego Padres for
Ryan Hanigan, whom the Padres had acquired earlier the same day. Middlebrooks competed with
Yangervis Solarte to be the Padres' starting third baseman in spring training. With Middlebrooks batting .212 on the season, the Padres optioned Middlebrooks to the
El Paso Chihuahuas of the Class AAA
Pacific Coast League (PCL) on July 22. On December 2, 2015, the Padres non-tendered Middlebrooks, making him a free agent.
Milwaukee Brewers On December 15, 2015, Middlebrooks agreed to a minor league contract with an invitation to spring training with the
Milwaukee Brewers. The Brewers assigned him to the
Colorado Springs Sky Sox of the PCL to start the 2016 season. Middlebrooks batted .282 with 10 home runs and 47 RBIs for Colorado Springs, before he was promoted to the major leagues on July 4. After batting .111 in ten games for Milwaukee, he went on the disabled list with a strained leg. The Brewers activated him from the disabled list and outrighted him off the 40-man roster on August 30.
Texas Rangers Middlebrooks signed a minor league contract with the
Texas Rangers on November 11, 2016. He began the 2017 season with the
Round Rock Express of the PCL. He spent most of 2017 with the Express until he was called up by the Rangers in September. He became the first player in over 100 years to hit a pinch-hit triple in both games of a doubleheader on September 6, 2017, against the
Atlanta Braves. In 22 games for Texas, Middlebrooks batted .211/.231/.368 with no home runs and three RBI. On October 10, Middlebrooks was removed from the 40–man roster and sent outright to Round Rock. He subsequently rejected the assignment and elected free agency.
Philadelphia Phillies On January 3, 2018, Middlebrooks signed a minor league contract with the
Philadelphia Phillies that included an invitation to spring training. On February 25, Middlebrooks broke his leg in a spring training game against the Orioles, and because of this injury, he did not appear in a game during the 2018 season. He elected free agency following the season on November 2, and on January 10, 2019, he announced his retirement. ==Broadcasting career==