Polk attended Guilford High School in Rockford, Illinois, where he was a standout linebacker for the Vikings football team. As a senior, he recorded 152 tackles, 13 quarterback sacks, 3 fumble recoveries, 3 blocked kicks and one interception.
He finished as one of the all-time leading tacklers in the state of Illinois high school history, with 453 career tackles, while also tallying 10 fumble recoveries, 7 blocked kicks, 5 interceptions and 30 tackles for loss. He received All-conference (three times), All-state, USA Today All-American and Northern Illinois Conference-9 Defensive Player of Year honors. He also practiced basketball.
Polk accepted a football scholarship from the University of Nebraska. As a freshman, he was a part of a team that shared the National Championship with the University of Michigan.
He became a starter at linebacker as a junior and was second on the team with 83 tackles, while tallying 12 tackles for loss (second on the team), 6.5 sacks (second on the team) and 21 quarterback hurries (led the team).
As a senior, he led the team with 90 tackles and also had 13 quarterback hurries (second on the team). He finished his college career with 227 tackles (14th all-time in school history), 32 tackles for loss (9th all-time in school history) and 10 sacks.
Polk was selected by the San Diego Chargers in the fourth round (112th overall) of the 2001 NFL Draft. As a rookie, he played 6 games on special teams, finishing with 4 tackles after being placed on the injured reserve list with a torn rotator cuff injury on November 14.
In his second season, he was voted by teammates as the Chargers Special Teams Player of the Year
, after leading the team with 13 tackles. He also registered his first-career safety and first-career blocked kick
. In 2003, he was voted as the Chargers co-Special Teams Player of Year, after tying for team lead with 16 tackles.
In 2004, he was declared inactive in the first game with a shoulder injury, he played in the second game against the New York Jets, only to be placed on the injured reserve list with a dislocated left shoulder on September 21. In 2005, he suffered an Achilles injury in the final off-season coaching session and was placed on the injured reserve list on July 28.
In 2006, he filled in for a suspended Shawne Merriman in the first 4 games. He went on to enjoy his best professional season, posting 32 defensive tackles, 2 sacks and 19 special teams tackles (second on the team) and received the team's Ed Block Courage Award.
In 2007, he started two games at inside linebacker in place of an injured Matt Wilhelm. On November 20, he was placed on the injured reserve list with a left shoulder injury he sustained in the November 18 game against the Jacksonville Jaguars, at the time he was leading the team with 11 special teams tackles. At the end of the year, he shared the team's Most Inspirational Player Award with Philip Rivers. Polk was released on August 30, 2008.
On October 16, 2008, Polk was signed as a free agent by the Dallas Cowboys, reuniting with head coach Wade Phillips, who was his defensive coordinator with the San Diego Chargers. He was signed for depth purposes after special teams player Sam Hurd was lost for the year with a high left-ankle sprain injury and Kevin Burnett was limited with a calf injury. He wasn't re-signed at the end of the year.
In 2009, he was the special teams coach at Grossmont College. From 2010 to 2012, he was a special teams assistant for the San Diego Chargers. In 2013, he was a coaching intern for the Dallas Cowboys. In 2014, he joined the Tampa Bay Buccaneers as an assistant special teams coach.