Since junior high school, Mustain has accumulated a record of 61–3 (.953) as a starting quarterback (9–1 in eighth grade in 2001, 9–0 in both ninth grade in 2002 and 10th grade in 2003, 12–1 in 11th grade in 2004, 14–0 in 12th grade in 2005, 8–0 as a freshman at Arkansas in 2006, 0–1 in 2010 at USC).
By the time he left Southwest Junior High School, Mustain was already the object of high expectations; however he did not start for the Springdale High School varsity team until late in his sophomore season.
In 2004 as a junior, Mustain was 139-of-222 for 2,169 yards and 20 touchdowns as Springdale posted a 12–1 record and reached the Arkansas Class 5A semifinals. He threw only five interceptions in 222 attempts and rushed for 350 yards and 14 touchdowns.
In 2005 as a senior, Mustain threw for 3,817 yards and set an Arkansas Class 5A single season record with 47 touchdowns and completed 69.3 percent of his pass attempts. Springdale went undefeated with a record of 14–0 and won the Arkansas Class 5A state title, including three wins over nationally ranked opponents and a No. 2 ranking in one national poll.
On January 7, 2006, Mustain was the starting quarterback for the West team in the U.S. Army All-American Bowl in San Antonio, Texas, where he was awarded the Hall Trophy as National High School Player of the Year.
PARADE named him High School Player of the Year in its January 1, 2006 issue. He was then named Mr. Football in Arkansas by the Arkansas Democrat-Gazette. He was also named the 2005–06 Gatorade National Player of the Year and the 2005 USA Today National Player of the Year, the first-ever from the state of Arkansas. Scout.com ranked him as the top high school recruit for the class of 2006. Mustain had told reporters he planned to play for either Notre Dame, Tennessee, Alabama, or his home-state Arkansas Razorbacks.
Mustain was the top quarterback in the nation coming out of high school in 2006, and was considered a better prospect than eventual Heisman-winner Tim Tebow. In recognition of his accomplishments, Springdale Mayor Jerre Van Hoose declared December 6, 2005 "Mitch Mustain Day" in the city.
In December 2005, Gus Malzahn, Mustain's coach at Springdale, was hired to be the new offensive coordinator at the University of Arkansas; this was widely taken to signal the Razorbacks willingness to shift their offense to adapt to Mustain's style of play. The hiring enabled the Razorbacks to recruit the highly touted quarterback. On January 16, 2006, Mustain informed Malzahn of his decision to commit to Arkansas, but only after Notre Dame Coach Charlie Weis opted to offer quarterback recruit Jimmy Clausen over Mustain. In addition to Malzahn, Mustain joined six of his high school teammates at Arkansas.
Mustain enrolled at the University of Arkansas on July 10, 2006 and, in his first game on September 2, 2006, replaced starting quarterback Robert Johnson in the fourth quarter of an eventual 50–14 loss to the USC Trojans. He immediately put together an 80-yard touchdown drive against the Trojan defense. The following day, Arkansas head coach Houston Nutt named Mustain as the starting quarterback for the next game against Utah State, moving Johnson to wide receiver.
Mustain accumulated a record of 8–0 as a true freshman starter, including a 27–10 win on the road over the #2 ranked Auburn Tigers on October 7, 2006, helping guide the Razorbacks to 11th in the college football rankings. The offense was oriented around what was considered among the nation's best running back tandems, Darren McFadden (who would be the runner-up for the Heisman Trophy), Peyton Hillis, and Felix Jones; as a result, Mustain's statistics did not match his high school numbers in a more pass-oriented offense.
A turning point occurred on November 4, 2006 in No. 11 Arkansas' 26–20 win over South Carolina, when Mustain was relieved after one series by sophomore Casey Dick, who led the Razorbacks for 228 yards and a touchdown. The day after the game, Dick was named the starting quarterback for an upcoming game against #13 Tennessee, with Coach Nutt citing "experience" as the primary reason for the change.
Mustain did not play in the next three games and entered for one series in the final game of the regular season, the SEC Championship game, on December 2, 2006, against the Florida Gators.
On December 20, 2006, Nutt announced that Dick would start for the Razorbacks in the January 1, 2007 Capital One Bowl against the Wisconsin Badgers; however, he stated that Mustain would also enter the game in the third series. The game resulted in a 17–14 defeat for Arkansas.
Mustain finished the season with 894 yards passing, completing 69 out of 132 passes with 10 touchdowns and nine interceptions.
On January 15, 2007, Gus Malzahn, the offensive coordinator and Mustain's former high school coach, announced he was leaving the Razorbacks to join the University of Tulsa. The day after Malzahn's announcement, January 16, 2007, Mustain requested permission to transfer to another university and it was, subsequently, granted by Coach Nutt. The announcement was one year to the day after Mustain had initially announced his decision to sign with the Razorbacks out of high school. Nutt had initially refused Mustain's request to transfer out. After the initial denial, Mustain went to two Arkansas boosters for guidance, and they and his mother, Beck Campbell, followed up with Nutt to ask for the transfer, which he then agreed to.
Mustain enrolled at the University of Southern California (USC) on May 21, 2007. He joined his former Springdale High School and Arkansas teammate, Damian Williams, who had transferred to USC the previous January. Mustain found the West Coast offense run at USC to be appealing; it differed from the spread offense run by Malzahn and appealed to his quarterback playing style.
Under NCAA transfer rules, Mustain sat out the 2007 season and served as the quarterback for the scout team. On December 19, 2007, he was rewarded with the Service Team Player of the Year (offense) award at the Trojan football team's annual awards banquet.
Mustain became eligible to play again for the 2008 season, with three years of eligibility remaining. During fall camp before the 2008 season, starter Mark Sanchez suffered a dislocated left kneecap while warming up for practice; the injury sidelined Sanchez and threw his availability for the season opener at Virginia (and beyond) into question. As a result, Mustain and redshirt freshman Aaron Corp began alternating repetitions with the first team offense and competing for the possible starting spot. After missing nearly three weeks, Sanchez was cleared to play in the opener on the final day of fall camp; Corp was selected as his back-up because he demonstrated a better command of the offense, however, head coach Pete Carroll stated the competition for the back-up spot would continue through the season. The competition resulted in Mustain regaining the second spot for some games and Corp for others throughout the season.
At the end of the 2008 season, Sanchez opted to forgo his final season and enter the NFL Draft, leaving the competition for the starting position in the 2009 season open between Mustain, Corp, and in-coming true freshman Matt Barkley, who like the other two also received major accolades as a high school player. By the end of spring practices, Mustain was placed third in the order behind Corp and Barkley.
Despite being relegated to third-string, Mustain continued to persevere and even tried out at the punter position to try to contribute to the team. By mid-season, better results in practice, and after an injury to Barkley led to a disastrous outing by Corp as the starting quarterback, Mustain had climbed to the second position behind Barkley.
After the 2009 season, Corp transferred to Richmond, and after off-season practices, Mustain became Barkley's back-up for the 2010 season. Before the season, Mustain was diagnosed and started treatment for attention deficit hyperactivity disorder (ADHD) and head coach Pete Carroll left to coach in the NFL and was replaced by Lane Kiffin, who stuck with Barkley as the starter. Mustain proceeded to back up Barkley until Barkley was injured in the next-to-last game of the season, allowing Mustain to start his first football game since playing at Arkansas in 2006. Starting in the Notre Dame rivalry game, Mustain put up 21-for-38 passes for 183 yards with one interception in a game that became known for a pass that was dropped: In the final two minutes of the game, Mustain threw an accurate pass to a wide-open Ronald Johnson that would have resulted in a touchdown and the probable win, but Johnson bobbled the ball and dropped it. Moments after the drop, Mustain threw his only interception of the game to seal the loss.
Despite the loss, Mustain felt a boost in confidence and stopped taking his ADHD medication, Vyvanse. He thought he could earn money by selling the medication illegally, and was caught and arrested on February 1, 2011. Eventually, he entered into a pre-file community service program in order to avoid a more severe sentence.
Mustain was rated the 24th best quarterback in the 2011 NFL Draft by NFLDraftScout.com.
Mustain went undrafted in the 2011 NFL Draft, and signed a 10-day free agent contract with the Hamilton Tiger-Cats of the Canadian Football League on June 1, 2011 to see if he could win a backup job. He was unable to impress and was released by the Tiger-Cats on June 10, 2011.
Mustain then applied to Marine Officer Candidates School and worked at a friend's car dealership in Bentonville before signing with a new team in September.
On September 30, 2011, Mustain signed with the Georgia Force of the Arena Football League.
In January 2013, Mustain signed with the San Jose SaberCats to backup legendary Arena Football League quarterback, Aaron Garcia. In April 2013, the Sabercats signed Russ Michna as their new starting quarterback, while Mustain remained the backup and Garcia was traded. Mustain replaced Michna on June 1, 2013 after Michna was injured and was able to make his first AFL start the next week while Michna was out.
Mustain's rookie option was exercised by the SaberCats in the offseason.
On January 27, 2014, Mustain was traded, along with Jabari Fletcher, to the San Antonio Talons in exchange for Joe Sykes. After starting the first three games of the season for the Talons, Mustain was placed on reassignment on April 1, 2014.
Stats from ArenaFan:
It was announced on February 9, 2012 that the Chicago White Sox had signed Mitch Mustain to a minor league deal. Mustain, who had not pitched since high school, threw a 90 mph fastball at a tryout in front of a White Sox scout in January 2012. While attending USC, Mustain commented to a reporter that he had considered once again pursuing baseball though he never played for the Trojans during his time there. Mustain reported to spring training with the White Sox on March 8, 2012. On June 19, 2012, Mustain made his minor league debut for the Bristol White Sox against the Bluefield Blue Jays. Throwing the 8th and 9th innings, Mustain gave up two hits and recorded two strikeouts in two scoreless innings. The White Sox lost 7–2 in the season opener. Mustain made eleven appearances with Bristol before moving on to the Kannapolis Intimidators, where he pitched in eight contests. Overall, he pitched in 19 games in 2012, going 2–2 with a 4.63 ERA, and one save.