Singleton attended Irvington High School. As a senior linebacker, he received second-team All-state, SuperPrepAll-American, All-area and All-county honors. He also played in the New Jersey North-South All-Star game. He accepted a football scholarship from Temple University. As a freshman, he appeared in 8 games, starting 6 at strongside linebacker, while recording 31 tackles and 1.5 sacks. He missed the final three games with a fractured right arm. As a sophomore, he was named the regular starter at strongside linebacker, tallying 74 tackles, one sack, 5 passes defensed, 5 forced fumbles and one blocked punt. As a junior, he was named the starter at middle linebacker, registering 151 tackles and becoming only the fourth player in school history to surpass 150 tackles in a season. He also added one sack, one pass defensed and one fumble recovery As a senior, he was a defensive captain at middle linebacker, posting 134 tackles, one interception, 5 passes defensed and 2 forced fumbles. He finished his college career as the school's third all-time leading tackler, while starting 39 out of 41 games. He also had 5 sacks, one interception, 11 passes defensed, 7 forced fumbles and one fumble recovery.
Professional career
Tampa Bay Buccaneers
Singleton was selected by the Tampa Bay Buccaneers in the fourth round of the 1997 NFL Draft. As a rookie, he played mainly on special teams, making 4 special teams tackles and 2 blocked punt, returning the one he blocked in the fifth game against the Arizona Cardinals for a touchdown. In 1998, he was a backup at strongside linebacker behind Jeff Gooch, collecting 18 tackles, one pass defensed and 4 special teams tackles. In 1999, he was a reserve behind Shelton Quarles, making 26 tackles, one interception, 2 passes defensed and 15 special teams tackles. He had one tackle in the Divisional Playoff Game win against the Washington Redskins, before fracturing his left ankle in the fourth quarter, forcing him to miss the NFC Championship Game against the St. Louis Cardinals. In 2000, he registered 32 tackles, one pass defensed, 11 special teams tackles, one forced fumble and one blocked punt. He suffered a knee injury in the 13th game against the Dallas Cowboys, which forced him to miss the final 3 contests of the regular season. In 2001, he posted 32 tackles, one sack, 2 passes defensed and 11 special teams tackles. In 2002, he was named the starter at strongside linebacker after Quarles was moved to the middle linebacker. He finished with 89 tackles, one interception, 3 passed defensed and 3 special teams tackles. He also contributed to the team having the league's top ranking defense and winning Super Bowl XXXVII.
Dallas Cowboys
On March 13, 2003, he signed with the Dallas Cowboys as a free agent to take over the starting strongside linebacker position, that was previously handled by the departed Kevin Hardy. He recorded 57 tackles, 7 quarterback pressures, 5 passes defensed, 3 special teams tackles, 2 interceptions and one returned for a touchdown. He also helped the team have the league's top ranking defense. In 2004, he had 57 tackles, one quarterback pressure, one pass defensed, 3 special teams tackles, one forced fumble and one fumble recovery. He missed the last 3 games after being placed on the injured reserve list with an abdomen injury on December 23. He was replaced with Scott Shanle. In 2005, the team switched to a 3-4 defense, but he was still able the remain the starter at the left outside linebacker position, until suffering a broken clavicle against the Arizona Cardinals during the week 8 and being placed on the injured reserve list on November 1. He appeared in 7 games, making 19 tackles, 3 quarterback pressures, 3 passes defensed, one interception and 4 special teams tackles. He was replaced with Scott Fujita. In 2006, he lost his starting job after Greg Ellis was converted from a defensive end into an outside linebacker, but was able to start 6 games after Ellis was lost for the season with an Achilles injury. He finished with 22 tackles, one sack, one pass defensed, 8 special teams tackles and one forced fumble. He wasn't re-signed at the end of the season.
