Drafted in the 13th round of the 1972 NFL Draft by the Cleveland Browns, Sipe spent the first two years of his career as a member of the team's reserve squad, seeing no action on the field. In 1974, Sipe started four games after helping the Browns come back from a 12-point deficit against the Denver Broncos on October 27. However, after winning just one of the four contests, he was replaced by Mike Phipps. The team's disastrous 1975 season saw Sipe enter the starting lineup after three consecutive losses in which the Browns were outscored 124-26. Sipe's three starts reduced the margin of defeat for the squad, but still resulted in a trio of defeats, sending him back to the sidelines. The following year, he finally moved into a consistent starting role following an opening game injury to Phipps on September 12, 1976. As the team's signal caller that season, he led them to a 9-5 record, a six-game improvement over the previous season. 1976 was the team's second year under head coach Forrest Gregg. During the first half of the 1977 season, he led the team to five wins in their first seven games. However, on November 13 of that year, Sipe suffered a season-ending shoulder injury at Three Rivers Stadium against the Pittsburgh Steelers in the second quarter of the team's 35-31 defeat. With Phipps gone to the Chicago Bears, the Browns turned to back-up quarterback Dave Mays, who went 1-3 as a starter. The 1977 also saw a head coaching change as Gregg was fired and defensive coordinator Dick Modzelewski took over for the final game. Sipe came back the following year to throw for more than 2,900 yards and 21 touchdown passes, but the team's overall inconsistency resulted in an 8-8 finish. Serving as the catalyst for many thrilling moments during the 1979 and 1980 seasons, Sipe helped the team earn the nickname "Kardiac Kids." The designation was in recognition of their tendency to produce heart-stopping comeback victories in the final minutes of many games. Over the course of these two seasons, Sipe led the Browns to eight comebacks and eleven game-winning drives in the fourth quarter or overtime. Sipe lead Cleveland to a 4-0 start in 1979, including a season opening overtime win over the New York Jets.
1980 MVP award winning season
In 1980, Sipe passed for 4,132 yards and 30 touchdowns, helping to lead the Browns to their first postseason berth since 1972. Individually, his efforts earned him the NFL MVP award and a selection to the 1981 Pro Bowl. At the end of the divisional playoff game the Browns played against the Raiders following the 1980 NFL season, the Browns trailed the Raiders with a score of 14-12. After the Browns forced the Raiders to turn the ball over on downs on their own 15-yard line, Sipe led the Browns back down the field, reaching the Raiders 13-yard line in 9 plays. With just 49 seconds remaining, the Browns could have settled for a game-winning field goal, but due to the brutally cold and windy weather in Cleveland that day Browns head coach Sam Rutigliano instead opted to pass the ball. Sipe attempted a pass to Browns Hall of Fame tight end Ozzie Newsome, but it was intercepted in the end zone by Raiders safety Mike Davis. That play brought the Browns' season to a heartbreaking close, while the Raiders went on to win Super Bowl XV over the Philadelphia Eagles. The play call - "Red Right 88" - would be immortalized in Cleveland sports infamy.
1981-82 seasons
Despite throwing for 3,876 yards the following year, Sipe was at the controls as the team staggered to a 5-11 mark. In 1982, Sipe and the Browns won just two of the team's first six games in the strike-marred NFL season, and Sipe was benched in favor of third-year signal caller Paul McDonald.
Sipe regained his starting role the following year, but angered Browns management by negotiating with New Jersey Generals of the United States Football League during the season. Sipe finished the season with 3,566 passing yards and 26 touchdown passes. Sipe had led Cleveland to a 9–7 record and the team just missed qualifying for the AFC playoffs. He then signed with the Generals and played for them in 1984, before concluding his career with the Jacksonville Bulls in 1985. Sipe's contract with New Jersey was a three-year deal for $600,000.
