The Seattle Seahawks allowed just 277 points (17.3 per game) during the 2015 regular season, thus becoming the first team since the 1970 AFL-NFL merger to lead the league in scoring defense in four consecutive seasons, per Elias Sports Bureau (via ESPN Stats & Info).
Unlike in 2012 and 2014, when the Seahawks led by at least 27 points, the scoring defense title came down to the wire in 2015, with the Cincinnati Bengals (279 points) finishing just two points behind Seattle. The Kansas City Chiefs (287 points) and Denver Broncos (296 points) were also within striking distance.
Entering Week 17, it seemed unlikely Seattle would capture the title, as the Bengals drew a favorable home matchup with the injury-ravaged Baltimore Ravens, whereas the Seahawks had a road game against the offensive powerhouse Arizona Cardinals.
Even with Arizona playing all of its starters, the Seattle defense somehow held the Cardinals to only six points, thus allowing the Carolina Panthers (500 points) to edge out the Cardinals (489 points) for the lead in scoring offense.
Arizona managed to finish as the NFL leader in total yards (6,533), further illustrating the impressive nature of Seattle's season-closing 36-6 victory.
Given the amount of defensive talent the Seahawks have under contract beyond 2015, it won't be at all surprising if the streak stretches to five years next season, though the immediate focus is obviously on beating the Minnesota Vikings in the Wild Card Round of the NFC playoffs.