Although mostly sidelined for the first several years of his NFL career, Sipe was eventually recognized as one of the better quarterbacks in Browns history, winning the league's Most Valuable Player Award in 1980.

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.

The 1977 season also saw a head coaching change as Gregg was fired and defensive coordinator Dick Modzelewski took over for the final game.

Serving as the catalyst for many thrilling moments during the 1979 and 1980 seasons, Sipe helped the team earn the nickname "Kardiac Kids."

With just 49 seconds remaining, the Browns could have kicked a game-winning field goal, but due to the brutally cold and windy weather in Cleveland that day, which made a field goal attempt significantly more risky than usual, Browns' head coach Sam Rutigliano instead opted to pass the ball.

That play brought the Browns' season to a heartbreaking close, while the Raiders went on to win Super Bowl XV over the Philadelphia Eagles.

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.

[4] Sipe lives in San Diego and coached the football team at Santa Fe Christian School in Solana Beach, California, where he helped the Eagles to four CIF titles and a combined record of 75–21–1.