Stalls attended Taft High School and did not start playing football until ninth grade, because he used to focus on ice hockey instead. After not receiving much interest and writing letters to 40 prospective schools, he received a scholarship offer from the Division II University of Northern Colorado. He was a four-year starter at defensive tackle and received third-team Little All-American honors in 1975. In 1997, he was inducted into the University of Northern Colorado Athletic Hall of Fame.
Stalls was selected in the seventh round of the 1977 NFL Draft by the Dallas Cowboys. As a rookie he was a core special teams player. In 1978, he was used mainly as a pass-rush specialist at left defensive tackle in place of Jethro Pugh or Larry Cole and emerged as a key reserve, registering 4 unofficial sacks. In 1979, he started the first 12 games at left defensive tackle ahead of former first-round draft choiceLarry Bethea, until being replaced by Cole, after the Cowboys traded for John Dutton who would play left defensive end. He finished with 51 tackles and 5 unofficial sacks. In 1980, Ed "Too Tall" Jones unretired and the Cowboys opened training camp with 8 quality defensive linemen, when they usually kept seven. The team decided to retain Bethea and Bruce Thornton instead, and on August 6, Stalls was traded to the Tampa Bay Buccaneers in exchange for a 1981 seventh round pick and a 1982 fourth round pick.
Tampa Bay Buccaneers
In 1980, the Tampa Bay Buccaneers traded for Stalls to replace an injured defensive end Wally Chambers. He appeared in 15 games with 3 starts. In 1981, he was a backup end and defensive tackle used mostly on passing downs, until injuries to Lee Roy Selmon and Bill Kollar's season ending knee injury, forced him to start 9 games at left defensive end. In the 1982 strike shortened season, he led the team in sacks ahead of the future hall of famer Selmon. The next year, he had a contract holdout during training camp and asked for the Buccaneers to trade him to the Denver Broncos, in order to pursue his veterinarian interests in the offseason. Complicating matters was a tense relationship with head coachJohn McKay and the team's ownership, because of his NFL players' union activities. Stalls ended up renegotiating his contract after the Broncos didn't accept giving up a fourth-round draft choice as part of the trade. He eventually reported to the team and had to pay $40,000 in fines for missing time. On October 18, he was waived after the Buccaneers were notified that he signed a future services contract with the Denver Gold of the United States Football League.
Los Angeles Raiders (first stint)
On November 10, 1983, needing help on the defensive line, the Los Angeles Raiders signed Stalls to a short-term contract after the Denver Gold agreed to loan him. Although he didn't have the size, he was used as a pass-rushing nose tackle where his quickness created mismatches en route to the Raiders winning Super Bowl XVIII.
Denver Gold (USFL)
Stalls took two weeks off after the Super Bowl to physically recover from the grind of the NFL season and joined training camp in February. In 1984, he led the team in sacks with 12.5 but his production started to decline halfway through the season because of his body exhaustion. On May 18, he announced his retirement to concentrate in his next career.
Los Angeles Raiders (second stint)
After sitting out the previous year attending veterinary school at Colorado State University, he was signed by the Los Angeles Raiders as a free agent on July 21, 1985. The team used him again as a pass-rush specialist from the nose tackle position. He was released on October 3.
