Arroyo made two starts and four relief appearances in the postseason, compiling a 0–0 record with two holds and a 7.82 ERA for the 2004 World Series champion Red Sox.

[7] Arroyo's most productive season came in 2005, when he posted career highs up to that time in wins (14), starts (32), innings (205.1) and pitching appearances (35).

Highlights of the season included a league-leading 240+2⁄3 innings pitched, a selection to the All-Star game, as well as his first career shutout in the major leagues.

After a sub-par first half of the 2009 season, Arroyo turned in an excellent second half, lowering his ERA from the 5's to the 3's, throwing multiple shutouts and complete games, and putting himself in position to be the Reds top starter in 2010 since Edinson Vólquez, the #1 starter in 2009, was out for the start of the season following Tommy John surgery.

On March 26, 2011, Arroyo was diagnosed with mononucleosis, a condition where there is a high lymphocytes count in the blood from an Epstein-Barr virus (EBV) infection.

Arroyo was chosen by Reds' manager Dusty Baker to start Game 2 of the 2012 National League Division Series versus the San Francisco Giants.

Although the numbers paint a picture of a subpar pitching year, Arroyo managed to throw one shutout and two complete games in his age 36 season.

[13][14] On June 16, Arroyo was placed on the disabled list for the first time in his career, after leaving a start early against the Dodgers with an elbow injury.

[15] It was announced on July 7 that Arroyo would be undergoing Tommy John surgery to repair a torn UCL, forcing him out for the remainder of the 2014 season.

[16] On July 30, 2015, in a three-team trade, the Los Angeles Dodgers acquired Arroyo, Mat Latos, Michael Morse, Alex Wood, Jim Johnson, Luis Avilán, and José Peraza, while the Miami Marlins acquired minor league pitchers Victor Araujo, Jeff Brigham, and Kevin Guzman, and the Braves received Héctor Olivera, Paco Rodriguez, minor league pitcher Zachary Bird and a competitive balance draft pick for the 2016 MLB draft.

[21] On February 2, 2017, Arroyo signed a minor league contract with the Cincinnati Reds that included an invitation to spring training.

[21][22] On June 19, Arroyo was placed on the 10-day disabled list with a right shoulder injury, and he admitted that he was contemplating retirement, stating "I don't see myself ponying it up next year.

"[23][24] Arroyo declined the opportunity to pitch one inning in September to close out his career, as he wanted to give a chance to a younger pitcher.

Prior to the game, a ceremony was held with video tributes from manager Bryan Price and singer Eddie Vedder.

[27] A day after reports claimed former Red Sox teammate David Ortiz was among 104 Major League players to have failed drug tests in 2003, Arroyo revealed he had used androstenedione and amphetamines in his career.

While this is considered below average speed among major league pitchers, his fastball had excellent movement and Arroyo was adept at "spotting" it.

From the stretch position with runners on base, his leg-kick was much less pronounced and his delivery to home plate was very quick by major league standards.

It included covers from bands such as Pearl Jam, Alice in Chains, Stone Temple Pilots, Foo Fighters and Incubus.

The album also includes the Red Sox victory song "Dirty Water" by The Standells, in which Arroyo is accompanied by Johnny Damon, Lenny DiNardo, and Kevin Youkilis.

He also taught Kevin Millar how to play guitar and performed vocals for the song "Tessie" as covered by the Dropkick Murphys.

[29] Bronson made his public debut on stage in January 2004 at the Hot Stove Cool Music fundraiser at the Paradise Rock Club in Boston.

In July 2020, Arroyo collaborated with classical pianist Harrison Sheckler to create a virtual choir recording of "Take Me Out to the Ballgame".

Current and former players, including Cy Young winner Bret Saberhagen, as well as announcers and other baseball personalities, were among the final 200 participants in the choir.