James Stewart Jr. aka Bubba Stewart, is a retired American professional motocross racer who competed in supercross riding the No. 7. Through his years of racing, he earned the nickname “The Fastest Man on The Planet”, due to his extraordinary, although sometimes daredevil-like, speed and abilities in motocross racing. Stewart has not been seen in any supercross events since 2015.

His father, James Sr., was a motocross enthusiast and introduced his son to the sport at the age of three. Stewart entered his first motocross race when he was four years old.

Having 84 amateur wins and 7 Loretta Lynn’s Amateur Championships all before the age of 16, he debuted as pro in 2002. While crashes and rookie mistakes kept him from winning the 2002 125 West Supercross title, he went on to dominate the 2002 125cc national championship and was named the 2002 AMA Rookie of the Year. He was also named one of "20 Teens Who Will Change the World" in the April 2003 issue of Teen People magazine.

Stewart went on to win the 2003 125 West Supercross Championship but suffered a severe crash at the season ending 125 East/West Shootout in Las Vegas, Nevada. With his collarbone broken in two places as a result of the crash, he was forced to sit out the first few rounds of the 2003 AMA Motocross series, losing the hope to win the championship, although he won every race he competed in after coming back from that injury.

In 2004 he won both the 125 East Supercross title and the 125 Outdoor national title, only losing one moto to Mike Brown in the latter due to a broken clutch cover.

On April 2, 2005, at Texas Stadium (in only his 3rd Supercross race), Stewart captured his very first Supercross victory. He would go on to record many more victories throughout 2005 and 2006, and he eventually won the 2007 Supercross Championship. He was unable to finish the 2007 National series due to a knee injury.

Stewart missed the last 15 races of the 2008 Supercross season due to a knee injury caused by a crash into Dale White #7.

Stewart signed with L&M Yamaha racing for the 2009 season, replacing Chad Reed for the supercross season. In the latter season Stewart and Chad Reed were involved in the tightest (and sometimes heated) points race of Stewart's career. Stewart won 11 of the 17 events. On May 2, 2009, at Sam Boyd Stadium in Las Vegas, Stewart won the 2009 Supercross Championship by a margin of 4 points over Reed (377-373).

After a strong charge by Supercross class rookie Ryan Dungey at the opening round at Anaheim, Stewart captured the lead on lap 18, going on to take the win . In round 2, Stewart was involved in a crash during his heat, but came back to win the Last Chance Qualifier. In the final, a collision with Chad Reed caused both riders to fall. Reed's left hand was pinned under Stewart and Reed pushed Stewart's head off his arm, in what some deemed to be a physically aggressive manner. Controversy followed in the pits when Stewart pushed Reed's bike off its stand, resulting in an official warning from the AMA. Still struggling with injury Stewart finished 3rd behind Ryan Dungey and Josh Hill in round 3. Stewart retired from the season after having surgery from Dr. Arthur Ting for a broken right scaphoid.

Stewart's wrist injury took longer than expected to heal, leaving him out of the 2010 Motocross series, although he did return for one round at Unadilla where he placed third in the first moto and retired early from the second moto, citing bike setup issues and exhaustion.

On January 8, 2011 Stewart made his return to Supercross placing 3rd in the Anaheim season opener. The next week at Phoenix on January 15, he won his first main event in over a year, leading all 20 laps over Ryan Villopoto, who trailed close behind for most of the race. Throughout the season Stewart suffered several crashes with his last big crash in the season finale at Las Vegas where he had the lead but then crashed in the whoops. He took out Kevin Windham along with him, allowing Villopoto and Reed to pass 

On March 10, 2012 Stewart claimed his 44th Supercross win by taking 1st place at Daytona International Speedway. At the end of the season, Stewart left Joe Gibbs Motocross Racing.

On January 5, 2013, after an unsuccessful finish of the 2012 AMA Motocross Series, Stewart made his return to Supercross with his new Yoshimura Suzuki bike. Although having a sore right knee and in pain, he finishes 8th in the Main Event at the Anaheim season opener. He got back up in Atlanta winning the main event, leading all 20 laps. Throughout the season, Stewart had several crashes, including at the Metrodome, in Minneapolis, where he had the lead in the Heat Race, but crashed in the rhythm section near the Mechanics Area. He did come back with a win in the LCQ. In the Main Event, Stewart was injured again, this time tweaking his wrist and retired on Lap 7. Consequently, Stewart was out for the remainder of the three rounds of the 2013 AMA Supercross Series.

On October 19, 2013 Stewart raced the Monster Cup for the first time at Sam Boyd Stadium in Las Vegas. Having a bad start in the first moto, he fought up to 8th. In the second moto he took the holeshot and was battling hard with Villopoto, beating Villopoto due to a hard crash on the Last Lap after missing the Joker Lane. In the third moto James fought hard past Ken Roczen and took the 3rd moto win. On the Final Lap, Stewart took the Joker Lane twice on second and third Motos, before crossing the finish line. He won the overall and the $100,000 payout.

Coming off an overall win in the Monster Energy Cup, Stewart was now a title threat for the 2014 Supercross Championship. On January 4, 2014 at Angel Stadium at A1 Stewart starts mid pack and works his way up to the leader Ken Roczen. With only 5 laps to go, he has a big crash in the whoops. He would finish seventeenth. At San Diego on February 8, he won his first main event for 2014 and went on to win 5 more main events, including a win in Toronto to pass Ricky Carmichael for second in all-time wins in Supercross. Stewart made the podium 8 times and finished the season in 3rd place.

Stewart was suspended for 16 months for failing an anti-doping test. Stewart, who is medically prescribed Adderall, failed to submit the proper paperwork for a Therapeutic Use Exemption (TUE). Stewart missed the entire 2015 Supercross season and the 2015 Lucas Oil Pro Motocross Championship series.

Following his suspension, Stewart returned to race the single-day Monster Energy Cup in Las Vegas, NV. After a crash in the first of three rounds however, Stewart did not start the following motos.

Stewart returned for Anaheim 1 at the start of the 2016 Supercross season. However, in the main event a first lap mishap by Ryan Dungey caused Stewart to crash. Stewart was knocked unconscious and suffered a concussion. Although no official retirement has been announced, Stewart has not returned to racing since this injury.

One day after announcing his split from JGRMX and Yamaha, Stewart signed to ride with Yoshimura Suzuki aboard their RMZ-450. Stewart won the first four motos of the season. However, during Round 3 of Thunder Valley in Colorado, Stewart was leading when a person ran across the track in front of him, causing him to crash. The result of the crash was a serious injury is his right hand breaking his wrist. Consequently, he was unable to finish the rest of the Motocross series due to the extent of the injury. Though he did come back at some point in Red Bud, but due to multiple injuries, Stewart will not race for the rest of the 2012 AMA Motocross Series until he gets 100% healthy.

The 2013 Season was a three-way battle with Stewart, Ryan Villopoto and Ryan Dungey. Chad Reed was thought to be the main show for the title, even though he struggled to ride hard and pass for the lead. Throughout the season, Stewart had several crashes including Motocross 338 in Southwick, Massachusetts, where he had the lead halfway through, but crashed in the sand section in Moto 1 ending up finishing in 34th place. He did come back to finish 4th in Moto 2 making him 5th place overall. Stewart struggles to ride hard, riding though a neck injury from a crash in the first corner at Unadilla.

Stewart made his X Games debut on July 30, 2009 at X Games XV, and placed second in the best whip competition with 21% of the votes winning his first X Games medal.

He suffered a deep bruise to his bone and muscle in his left shoulder during seeding trials for SuperMoto on July 31, forcing him to drop out of the games.

On March 28, 2010 Stewart's reality show “Bubba’s World” debuted and ran 10 episodes. The show got mixed reviews, due in part to Stewart’s somewhat self-centered actions throughout the show. The second season started in December, offered 13 episodes and concluded Feb. 24. There has been no announcement about a third season.

In October 2011, Stewart signed to race for Joe Gibbs Racing, with a multiyear contract to run for JGRMX in motocross as well as plans to run NASCAR stock car races in the K&N Pro Series East and Nationwide Series. At the end of the 2012 Supercross Season, Stewart left Joe Gibbs Racing and JGRMX. Stewart said that he would be open to racing with Gibbs in the future, but stated that he wanted to get back to being competitive in motorcycle racing, and that a change was necessary.

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