query: When did the NFL first introduce its television blackout policies?
passage: National Football League television blackout policies
From 1973 through 2014, the NFL maintained a blackout policy that states that a home game cannot be televised in the team's local market if 85% of the tickets are not sold out 72hours prior to its start time. This makes the NFL the only major professional sports league in the US that requires teams to sell out tickets in order to broadcast a game on television locally. Although nationally televised games in the other leagues are often blacked out on the national networks on which the game is airing in the local markets of the participating teams, they can still be seen on the local broadcast TV station or regional sports network that normally holds their local/regional broadcast rights. The league blackout policy has been suspended on a year-to-year basis since 2015.
passage: National Football League television blackout policies
Their decision on whether to show home games typically depends on whether the NFL-designated local team is perceived to be the most popular in the market. For example, Harrisburg, Pennsylvania is a secondary market to the Baltimore Ravens; therefore the Harrisburg market's CBS affiliate, WHP-TV, must show all Ravens away games. However, since there are many Pittsburgh Steelers fans in the region, when the Ravens are home at the same time the Steelers are playing, that station shows the latter game. Harrisburg is thus considered a battleground territory for the Steelers–Ravens rivalry.