The NFL introduced the salary cap in 1994 with a cap of $34.6 million. The 2015 salary cap was the highest it has ever been with a cap of $143.28 million.
The salary cap is adjusted every year based on the league's revenues. The signing of the collective bargaining agreement in 1994 prompted the cap. The 1994 collective bargaining agreement lasted until 2009, but the team owners opted out in 2008, resulting in an uncapped 2010 NFL season, as the signing of a new collective bargaining agreement did not occur until 2011. Despite the lack of salary cap in 2010, many teams spent their money as if there was still a salary cap in place since the NFL warned them that a salary cap would soon return.
The salary cap in 2011 was $3 million less than what it was in 2009, but it has risen at a much faster rate during the span of the collective bargaining agreement signed in 2011 than it did during the period of the collective bargaining agreement signed in 1994. The salary cap has jumped at least $10 million in one offseason four times, as of 2015, with $10 million dollar jumps occurring in consecutive years between the 2013 and 2015 seasons. The largest jump the salary cap ever made was between the 2005 and 2006 season at $17.2 million.