Leaf had a successful college career at Washington State University, where he was a finalist for the Heisman Trophy his junior year. At Washington State University, Leaf was a member of Alpha Kappa Lambda, fraternity. He was selected as the second overall pick in the 1998 NFL Draft after Peyton Manning of the University of Tennessee, after which many scouts predicted that Leaf would have a successful career in the league.
However, despite his athleticism, his time as a professional was short and marked by injuries, poor media relations, and poor performance. A movie about his short career is being made. He is widely regarded as one of the biggest flops in NFL and professional sports history.
That year, Leaf was a finalist in balloting for the Heisman Trophy, given annually to the "most outstanding" player in American college football, as voted by media figures and former players. He finished third in the voting, behind winner Charles Woodson of Michigan and fellow quarterback Peyton Manning of Tennessee. He was also selected as the Pac-10 offensive player of the year, was a first-team All-American, and had the second-best national passer rating. Following the Rose Bowl, Leaf announced that he would forgo his senior year at Washington State and turn professional.
There was some debate leading up to the draft as to whether Leaf or Manning should be selected first. At 6-foot-5 and 240 pounds, Leaf was bigger and stronger, but most analysts agreed that Manning was the more mature player and the consensus top choice. However, differences in potential between the two seemed small enough that most observers expected it would not greatly matter whether a team selected Manning or Leaf.
On draft day, Leaf was selected second by the San Diego Chargers; Manning was selected first by the Colts. Other quarterbacks in that year's draft included current NFL quarterbacks Brian Griese and Matt Hasselbeck. Following the draft, the Chargers signed Leaf to a four-year contract worth $31.25 million, including a guaranteed $11.25 million signing bonus. It was, at the time, the largest signing bonus ever paid to a rookie. Shortly after being drafted, Leaf declared, "I'm looking forward to a 15 year career, a couple of trips to the Super Bowl, and a parade through downtown San Diego."
However, in the third game of the season, Leaf completed one of fifteen passes for 4 yards and fumbled three times in a loss against the Kansas City Chiefs. He was benched after throwing two touchdown passes and thirteen interceptions in nine games, and replaced by quarterback Craig Whelihan. After ten games, Leaf had thrown two more interceptions, passing for a total of 1,289 yards, with a 45.3 percent completion rate and a paltry passer rating of 39.
Leaf had poor relationships with the media and his teammates. In one infamous locker room incident during Leaf's rookie year, he was caught on-camera screaming at San Diego Union Tribune reporter Jay Posner, "Just fucking don't talk to me, all right! Knock it off!" and had to be physically restrained by teammate Junior Seau. Another on-camera incident involved Leaf confronting a heckling Chargers fan during a practice session. Two coaches had to restrain Leaf and escort him off the field.
Leaf missed his entire second season because of a shoulder injury uncovered by a preseason physical. He was placed on injured reserve but made headlines for getting into a heated shouting match with Chargers general manager Bobby Beathard and another coach. The incident resulted in a fine, a suspension without pay, and Leaf apologizing four weeks later.Leaf also allegedly lied about a hand injury to get out of practice so he could play golf instead. His suspension did not end his off the field troubles. While serving his 4 game suspension, a video surfaced of Ryan Leaf playing flag football in Ocean Beach, California while he was supposed to be rehabilitating his shoulder and wrist injuries. This incident marked the beginning of the end for Ryan Leaf in San Diego. After the video surfaced, the Chargers filed a grievance against Ryan Leaf citing a breach of contract for participating in activities detrimental to the team. The Chargers sought to recover $2.95 million of his $11.25 million signing bonus as well as use the incident as leverage to shorten the length of his contract. Despite the turmoil between Leaf and the Chargers front office, Leaf would remain with the Chargers into the 2000 season.
Leaf started the first two games of the 2000 season, only to complete less than half of his pass attempts, and throw for five interceptions and one touchdown. When backup Moses Moreno went down with a strained knee ligament, the Chargers gave Leaf more playing time. However, he injured his wrist while throwing an interception in a week four game and did not play again until week eleven. Following more poor performances and injury problems, he was released by the Chargers after the season, with a record of only four wins as a starter in three years.
Leaf attempted a comeback with the Dallas Cowboys, who signed him a few weeks after the Buccaneers released him. He failed his first physical and had trouble passing the second because of his wrist. The Cowboys released him in May 2002, after he had appeared in four games—all losses—and thrown for 494 yards with one touchdown and three interceptions. Leaf was signed days later to a one-year contract by the Seattle Seahawks who, like the Buccaneers, planned to let him develop slowly so he could heal from his injuries. The quarterback attended the team's spring minicamps and seemed upbeat about his new team. However, Leaf retired at the age of 26, just before the start of the Seahawks' 2002 training camp, initially offering no explanation, but later citing his injuries.
During his brief career in the NFL, Leaf appeared in 25 games and made 21 starts. He completed 315 of 655 passes for 3,666 yards, with 14 touchdowns and 36 interceptions. Leaf's career passer rating was 50.0, much lower than the 78.9 league average between 2000 and 2003.
In February 2001, Leaf married a Chargers cheerleader, Nicole. They separated two years later and divorced soon after. In February 2005, Leaf was enrolled in a sports management class called "Media Relations" at Washington State University. He graduated with a bachelor's degree in arts and humanities in May 2005.
Leaf joined Don Carthel's West Texas A&M staff as a quarterback's coach in 2006, and also became the school's golf coach in 2007. Said Leaf: "I feel very honored to be a part of Coach Carthel's staff and a part of an up-and-coming successful program. [...] About a year after I retired from playing, I decided that I wanted to get back to college, where I had the greatest time of my life, and to get involved with college football." Leaf also admitted that he was unprepared for the NFL when he was drafted back in 1998.
In April 2008, ESPN described Leaf as having made peace with his infamous NFL past: "When playing football became a job, it lost its luster for me. I kind of got out of the spotlight and life's never been this good.