As a junior baseball player, he hit .457 and led Tampa Catholic to a state championship. Prior to his senior baseball season, Baseball America ranked him the 20th-best high school prospect in the nation.[1]
Kelly was named the starting quarterback ahead of the 1999 season.[2] Due to his being named the starter, head coach Butch Davis was increasingly pressuring Kelly to focus exclusively on football.[5] Kelly led the team to the number 19 ranking in the AP Poll until he was injured during a game against second-ranked Virginia Tech.[3][6] Freshman backup quarterback Ken Dorsey excelled in Kelly's absence. When Kelly was cleared to return for the 2000 Gator Bowl, Butch Davis told him that, despite a stated policy that players could not lose their starting roles due to injury, Dorsey would be getting the start.[3] Kelly ultimately led the Big East Conference in passing touchdowns and interceptions thrown despite having missed three full games.[7]
Just over a month later, Kelly announced that he would be leaving Miami to focus on his baseball career due in part to the perceived financial security offered by a professional baseball career as well as his worsening relationship with Miami and Butch Davis.[3]
In February 2000, the Devil Rays restructured their agreement with Kelly and signed him to a four-year, $2.7 million contract to incentivize him to step away from football and focus on baseball. He began the season in Double-A with the Orlando Rays.[5] Prior to the season, Baseball America had ranked him the 100th-best prospect in baseball.[9] He spent the majority of the season in Double-A and led the Southern League in caught stealing with 21.[10]
On April 4, 2001, the Seattle Mariners purchased Kelly's contract from the Devil Rays, a move necessitated by the club's financial straits; the Devil Rays at the time owed him $1 million.[12][14][15] Kelly spent the following two seasons in Seattle's farm system.[9] Prior to the 2002 season, Kelly was described in the Seattle Post-Intelligencer as the Mariners' best outfield prospect.[15] Nonetheless, Kelly failed to reach the Major Leagues with the Mariners and was removed from the 40-man roster following the 2002 season. Seattle re-signed Kelly to a minor league contract in 2003 but sent him at the trade deadline to the New York Mets in exchange for Rey Sanchez.[16]
Kelly finished the 2003 season in Triple-A with the Norfolk Tides.[9] In 2004, he was invited to Major League spring training with the Mets who still considered him a prospect.[17] The Mets nonetheless released Kelly on April 3, 2004. He was picked up by the Cincinnati Reds three days later.[12] Kelly spent the season in Cincinnati's farm system.[9] In November 2004, the club re-signed him to a minor league contract.[18]
On June 12, 2004, Kelly appeared in a Major League game for the first time in nearly five years. In the same game, he recorded his first Major League hit, driving in Ken Griffey Jr. and Adam Dunn with a single against Todd Williams of the Baltimore Orioles.[19][20] He appeared in five more games with the Reds before undergoing arthroscopic knee surgery to repair a torn meniscus.[19][21] He was activated from the disabled list on July 14, 2005, and appeared in one more game with the Reds.[19][22]
On July 20, 2005, the Washington Nationals claimed him off waivers from the Reds.[23] On September 2, 2005, the Nationals called him up to the majors.[24] Kelly finished the season on the roster and appeared in what would be the final 17 games of his Major League career.[12]
Kelly's first child, a daughter named Jeneisha, was born when Kelly was only 16 years old.[17] In 1999, he was paying child support in the amount of $800 per month.[2] By the time he left Miami, he had two children and was married.[15] In 2002, Kelly married Adrian McPherson's first cousin once removed.[25] As of February 2004[update], he had three children.[17]
In June 2018, Kelly made his debut as a professional jai alai player. At the same time, he was serving as a part-time assistant football coach at Florida International University.[28]
Kelly has worked as a color analyst for college football broadcasts.[29]