Byron Antron Leftwich (born January 14, 1980) is an American football coach and former quarterback who played in the National Football League (NFL) for 10 seasons. He played college football for the Marshall Thundering Herd, winning MAC Most Valuable Player twice between 2001 and 2002. Leftwich was selected seventh overall in the 2003 NFL draft by the Jacksonville Jaguars, where he held a starting role during his first four seasons. He spent the remainder of his career as a backup for the Atlanta Falcons, Pittsburgh Steelers, and Tampa Bay Buccaneers and was a member of the Steelers team that won Super Bowl XLIII.

Following his retirement, Leftwich began a coaching career in 2016 under Bruce Arians with the Arizona Cardinals. He rejoined Arians as the offensive coordinator of the Buccaneers, a position he held from 2019 to 2022, and helped the team win Super Bowl LV. Leftwich was named an assistant coach for the Colorado Buffaloes in 2025.

Leftwich attended Howard D. Woodson High School in Washington, DC, and was a letterman in football, basketball, and baseball. He garnered an honorable mention on The Washington Post's All-Met football team in 1997 as a senior. Leftwich was also first-team All-DCIAA East in basketball his senior year.

Leftwich starred at Marshall University in Huntington, West Virginia. He was the MVP of the 2000 Motor City Bowl. Leftwich gained recognition after quarterbacking a 64–61 overtime victory over East Carolina in the 2001 GMAC Bowl, in which he competed against future teammate David Garrard. He is also remembered for being carried by linemen Steve Sciullo and Steve Perretta after breaking his shin, specifically the left tibia, and returning to the game, taking Marshall down the field on multiple series as he rallied his team to a 17-point comeback against Akron in November 2002, although Marshall still lost 34–20.

Because ESPN began broadcasting Mid-American Conference (MAC) games on Tuesdays and Wednesdays—days without other football on television—in 2000, nationwide "MACtion" audiences watched Leftwich's teams. Leftwich, along with fellow Marshall alumni Chad Pennington, Randy Moss, and Doug Chapman, are credited for helping the MAC gain more national attention; Marshall is now a member of the Sun Belt Conference. In his career at Marshall, Leftwich completed 939 of 1,442 passes (65.1 percent) for 11,903 yards, 89 touchdowns and 28 interceptions. He amassed 12,090 yards of total offense on 1,632 plays, ranking second on the school's all-time list behind Pennington.

Publicity from MACtion games helped make the obscure Leftwich a top ten draft selection. At the 2003 NFL draft, the Minnesota Vikings and Baltimore Ravens agreed to a trade to move the Ravens into position to take him with Minnesota's seventh overall selection. However, one of the teams had second thoughts at the last minute and the Vikings missed the allotted time for their pick. As a result, the Vikings had defaulted on their selection and consequently moved back to the ninth pick. The Jaguars, who were originally slotted to be drafting eighth overall, were taken up to the seventh pick, and they used it to take Leftwich.

Leftwich took over as the Jaguars starting quarterback in game four of his rookie year after Mark Brunell was injured in the previous week's matchup against the Indianapolis Colts.

For the first 10 games of the 2005 regular season, Leftwich was developing into the quarterback the Jaguars believed he would become when they picked him in the first round. He attained a passer rating of 89.3, ninth-best in the NFL, and a 3:1 touchdown-to-interception ratio (15:5).