He was a highly sought after two-sport athlete in the country following his senior season at Southern University Laboratory School in Baton Rouge.

He was named first-team Class 1A all-state selection on both offense and defense following his senior season, becoming the first player to be honored on both in Louisiana since 1991.

Spears attended Louisiana State University, where he played for coach Nick Saban's LSU Tigers football team from 2001 to 2004.

Playing against the Oklahoma Sooners for the national championship in the Sugar Bowl, Spears returned an interception 20 yards for a touchdown to give the Tigers a 21–7 advantage in their 21–14 victory.

He also recorded 21 quarterback pressures to help the Tigers finish the year third in the country in total defense.

In April 2021, Spears was inducted into the Louisiana High School Athletic Association Hall of Fame.

Spears was considered by head coach Bill Parcells to be the key to the team's eventual move to a 3–4 defense and wanted to take him with the first selection (11th overall pick).

[6][7] In his NFL debut at the San Diego Chargers, Spears was in the defensive line rotation but did not record a tackle.

He helped limit the Philadelphia Eagles to 129 yards, including just 19 rushing, the fourth lowest in franchise history.

He officially moved into the starting lineup full-time against the Arizona Cardinals and led all linemen with four tackles.

Spears logged his third career start in Philadelphia and posted a season-high seven tackles to lead all linemen and finish second on the team.

Three plays later, Drew Bledsoe completed a pass to Jason Witten for a touchdown and a 17–14 halftime lead.

Before the 2006 season, Spears underwent minor knee surgery to repair meniscus damage,[8] which forced him to miss the first two weeks of training camp.

The Cowboys moved to a 3-4 defense and Spears earned the starting role at left defensive end, finishing ninth with 48 tackles (31 solo), one sack, three pass deflections, two tackles for loss and tied for fifth on the squad with three quarterback pressures.

After the Cowboys' bye week, Spears led all defensive linemen with four tackles against the Tennessee Titans.

The Titans, in rookie quarterback Vince Young first career start, only rushed 27 times for 78 yards.

Spears had three tackles in the Cowboys' Christmas Day loss to the Eagles and did not record a stat in the season finale against the Detroit Lions.

In the Cowboys lone playoff game against eventual Super Bowl XLII champion New York Giants, Spears recorded two tackles.

Spears registered a tackle and three pressures in the wildcard playoff win against the Philadelphia Eagles, with the defense not allowing a rushing first down for the first time in postseason team history.

He was used mostly on running downs and registered 29 tackles (one for loss), 15th on the team and fifth among defensive linemen, one sack, two pass deflections and one quarterback pressure.

In the spring, Spears was a co-chair, along with teammate DeMarcus Ware, for the second annual Taste of the NFL: The Ultimate Dallas Cowboys Tailgate Party at Abacus restaurant that benefited The North Texas Food Bank.

[citation needed] He is a regular contributor to the Paul Finebaum Show, broadcast daily on the SEC Network.

[citation needed] Beginning with the 2017 college football season, Spears began hosting Thinking Out Loud on the SEC Network with former Alabama quarterback Greg McElroy.