(CNN) -

Here's a look at what you need to know about lockouts and strikes in professional sports. A lockout is imposed by management or the owners. A strike is initiated by the employees or players.

National Football League (NFL) Lockouts & Strikes: There have been six NFL work stoppages.

March 12-July 25, 2011 - The 136-day lockout, the longest work stoppage in NFL history.

Timeline of NFL Lockouts & Strikes: July 3-July 15, 1968 - The NFL Players Association votes to strike, and the NFL owners counter by locking out the players during training camp. The two sides come to an agreement regarding pension benefits, resulting in the first NFL collective bargaining agreement.

July 13-August 3, 1970 - In response to NFL veterans being locked out of training camp, the NFL Players Association votes to strike. The second NFL work stoppage ends with a four-year, $19.1 million deal.

July 1-August 10, 1974 - The 41-day strike ends when the veteran NFL players report to training camp without a new agreement.

September 21-November 16, 1982 - The 57-day strike is over revenue sharing. Play resumed on November 21.

September 22-October 15, 1987 - A 24-day strike. After the NFL players go on strike over free agency they are supplanted by replacement players.

March 8, 2006 - The collective bargaining agreement is extended through the 2011 season. Under the agreement, of the $9 billion revenue stream, NFL owners take $1 billion off the top for expenses. After that, the players get about 60%.

May 20, 2008 - The owners vote to end the collective bargaining agreement after the 2010 season.

February 18, 2011 - The NFL and the NFL Players Association (NFLPA) enter into federal mediation. George Cohen is the Director of the Federal Mediation and Conciliation Service (FMCS), an independent government agency handling the mediation.

March 3, 2011 - The existing contract between the NFL and the players expires at 11:59 pm EST.

March 4, 2011 - The negotiating deadline is extended by one week.

March 11, 2011 - Negotiations to draft a new collective bargaining agreement break down. At 4:40 p.m. EST, the players' union walks out on negotiations.

March 11, 2011 - After the NFLPA walks out on negotiations, the players decertify the union so that they can file a class-action antitrust lawsuit against the National Football League (Brady v NFL). Quarterbacks Tom Brady, Drew Brees, Peyton Manning are three of 11 football players who file the lawsuit on behalf of the players against the NFL.

March 12, 2011 - NFL lockout begins at midnight ET.

April 25, 2011 - U.S. District Judge in St. Paul, Minnesota Susan Richard Nelson rules in favor of the players, ordering the owners to end the lockout.

April 27, 2011 - Judge Nelson denies the NFL's appeal.

April 29, 2011 - The lockout goes back into effect as the league's appeal for a temporary stay of the ruling is granted by the 8th U.S. Circuit Court of Appeals.

July 21, 2011 - NFL owners vote 31-0 (Oakland Raiders abstain) to ratify the proposed 10-year collective bargaining agreement.

July 25, 2011 - The NFL players unanimously vote to ratify the collective bargaining agreement, effectively ending the 136-day lockout.

August 4, 2011 - NFL players ratify a new collective bargaining agreement, formally ending the labor dispute.

National Basketball Association (NBA) Lockouts: July 1-September 18, 1995 - The 80-day lockout revolves around the players dissatisfaction with their union and salaries.

July 1, 1998-January 6, 1999 - The 191-day lockout is over collective bargaining.

July 1-December 8, 2011 - The 161-day lockout ends when NBA players and owners agree to a 10-year collective bargaining deal.