He played in Major League Baseball (MLB) for the Oakland Athletics, Colorado Rockies, Baltimore Orioles, Arizona Diamondbacks, and Seattle Mariners.

[5] Byrnes regularly competed in baseball and football against Serra High School's Tom Brady, and Bellarmine College Prep's Pat Burrell.

At UCLA (1995–98), Byrnes hit second in the batting order and played right field in a lineup that featured future major-league stars Troy Glaus (1995–97) and Garrett Atkins (1998).

[6][7] He was again selected in the Major League Baseball Draft, this time by the Houston Astros after his junior season, but again elected to stay in school.

That season, he played for the Class-A Advanced Modesto A's, and the Double-A Midland RockHounds and in 139 combined games, Byrnes batted .306 with 42 doubles, 1 triple, 7 home runs, 88 RBIs, and 34 stolen bases.

This play was then followed up by Red Sox third baseman Bill Mueller running into Miguel Tejada as Byrnes was rounding third (later in the same inning).

On July 13, 2005, Byrnes, along with prospect Omar Quintanilla, was traded to the Colorado Rockies for pitchers Joe Kennedy and Jay Witasick.

[14] In 52 games with the Orioles that season, Byrnes batted .192 with 7 doubles, 1 triple, 3 home runs, 11 RBIs, and 3 stolen bases.

In his combined totals that season between the Oakland Athletics, the Colorado Rockies, and the Orioles, Byrnes batted .231 with 22 doubles, 3 triples, 10 home runs, 35 RBIs, and 5 stolen bases in 111 games.

[19] At the end on the season, Byrnes batted .286 with 30 doubles, 8 triples, 21 home runs, 83 RBIs, and 50 stolen bases in 160 games.

[citation needed] Byrnes returned to the team on June 23, 2008, batting leadoff against the Boston Red Sox at Fenway Park.

[citation needed] At the end of the 2008 season, Byrnes batted .209 with 13 doubles, 1 triple, 6 home runs, 24 RBIs, and 4 stolen bases in 52 games.

[23] He was injured during a game against the Texas Rangers after opposing pitcher Scott Feldman hit Byrnes on the hand with a pitch.

[24] He played 16 minor league games during his rehab stint with the Triple-A Reno Aces, batting .279 with seven doubles, one triple, two home runs, nine RBIs, and one stolen base.

[3] Byrnes said this about being signed by the Mariners: Speaking with Jack [Zduriencik], the role wasn't necessarily specified other than the fact that he believes that I would contribute.

After the game concluded with yet another Mariners loss, Byrnes stormed out of the clubhouse and out of Safeco Field on his bicycle, passing General Manager Jack Zduriencik in a fury.

[27] Byrnes was released by the Mariners on May 2, 2010, after batting .094 with three hits in 32 at-bats, one run scored, two doubles, nine strikeouts, and six bases on balls in 15 games on the season with Seattle.

[28] In a press release by the Mariners, general manager Jack Zduriencik said that, "Eric Byrnes is a tremendous competitor and a credit to baseball.

He currently lives in a closed community at Half Moon Bay, California, with his wife Tarah and daughter; Byrnes plays slow pitch softball and golf.