Last season, the Broncos were defined by having one of best defenses in NFL history: After a dominant regular season, Denver’s defense carried the team to a Super Bowl title. The defense was particularly dominant against the pass, allowing just 5.1 yards per pass play to opposing offenses. But this year? The defense is, remarkably, even better.

Let’s begin with a refresher on just how good last year’s pass defense truly was. On average, NFL teams in 2015 gained 6.4 net yards per pass attempt (net yards includes yards lost to sacks), meaning the Broncos defense was 1.3 net yards per attempt better than average. That was the 20th-best mark of any team from 1970 to 2015, and Denver was the seventh team in that group to win a Super Bowl:

TEAM YEAR NET Y/A OF OPPONENTS VS. NFL AVG. PLAYOFF RESULT NET Y/A NEXT SEASON GMS 1-8 1 Minnesota 1970 3.46 -2.05 Lost Div -1.48 2 Pittsburgh 2008 4.30 -1.86 Won SB -0.77 3 Miami 1982 4.03 -1.81 Lost SB -0.66 4 Miami 1973 3.51 -1.77 Won SB 0.74 5 Minnesota 1989 4.47 -1.64 Lost Div -0.19 6 Pittsburgh 1974 3.75 -1.60 Won SB -1.25 7 New York 2009 4.61 -1.55 Lost Conf -0.37 8 Dallas 1977 3.69 -1.49 Won SB -0.09 9 Pittsburgh 2011 4.87 -1.45 Lost WC -1.05 10 Minnesota 1975 3.99 -1.45 Lost Div -1.49 11 New Orleans 1992 4.35 -1.43 Lost WC -0.54 12 Tampa Bay 1979 4.36 -1.40 Lost Conf 0.63 13 Minnesota 1971 4.18 -1.39 Lost Div -1.19 14 Tampa Bay 2002 4.50 -1.38 Won SB -0.82 15 Oakland 1975 4.07 -1.38 Lost Conf 0.85 16 Seattle 2013 4.85 -1.36 Won SB -0.19 17 Los Angeles 1980 4.60 -1.36 Lost WC -0.58 18 Atlanta 1977 3.82 -1.36 — -1.08 19 Philadelphia 1991 4.62 -1.35 — -0.32 20 Denver 2015 5.11 -1.30 Won SB -1.73 The Broncos defense is good

Football studies have generally shown that offenses are more consistent from year to year than defenses, and regression to the mean is always a key part of any analysis for a historically great unit. As a result, we wouldn’t expect Denver’s 2016 pass defense to be anywhere near as good as the 2015 one. And that’s exactly what you see with most of the other teams on the list above.

The other pass defenses on the top 20 list above were, on average, 1.53 net yards per attempt better than average against the pass in their dominant season; however, in their first eight games of the following season, they were just 0.52 NY/A better than average. That’s a sign of how difficult is it for dominant defenses to sustain that level of excellence over a long period. Defensive backs and pass rushers are two of football’s most health-dependent roles, and even one player losing a step or leaving in free agency can sink a unit. But so far this season, the Broncos have been even better that last season, jumping from 1.30 NY/A better than league average to 1.73.

There are three main variables determine a defense’s NY/A average, and Denver is great in all three areas:

1. Sack rate

This year’s Broncos have taken down opposing passers on 8.4 percent of all pass plays, the third-best rate in the NFL behind the Bills and Eagles. The Broncos blitz a lot — in fact, on a league-high 38.6 percent of passes — and the team has pressured the quarterback on a league-high 50 percent of all blitz plays. But Denver has been great when not blitzing, too: The Broncos lead the league with a 10.2 percent sack rate on passes when not sending extra pressure. Von Miller is the star, of course, and his 8.5 sacks rank second in the NFL. But Derek Wolfe and Shane Ray have combined for 8.5 sacks, too, and the defense is even scarier now that DeMarcus Ware (two sacks in the first two games) is back from injury.

2. Completion percentage

Last year, Denver’s pass defense allowed 60 percent of passes to be completed, which ranked eighth in the league; this season, Denver has allowed opposing passers to complete just 53.5 percent of all passes, easily the best rate in the league through eight weeks. And on passes to wide receivers, Denver’s at 49.6 percent, the only defense in the league holding opposing wideouts to a rate under 50 percent.

The Broncos are blessed to have two of the best cornerbacks in the game in Chris Harris and Aqib Talib. According to Pro Football Focus (link requires subscription), those two rank as two of the best three corners in the NFL this season, both overall and in pass coverage. And while the loss of linebacker Danny Trevathan (and pass rusher Malik Jackson) was supposed to harm the defense, linebacker Brandon Marshall and safeties T.J. Ward and Darian Stewart have helped mitigate any damage. Denver ranks seventh in completion percentage on passes to tight ends at 59.7 percent, which nearly matches last year’s production (59 percent, fourth).

3. Yards per completion

Even when opponents completed passes last year against Denver, they didn’t usually go for much, gaining only 10.3 yards on average, a hair behind Cincinnati for the league lead. The Broncos defense is again one of the leaders in this category, allowing only 10.7 yards per completion. Any decrease in this category is more than offset by the improved rate on completed passes, but another key is that the Broncos aren’t allowing opponents to do much after the catch. This season, opposing receivers have gained just 4.2 yards per catch after making the reception, fourth-best in the league. In other words, on the rare occasion when receivers do make a reception, they generally get tackled pretty quickly.

The Broncos pass defense guided the team to a championship last year, helping shut down Ben Roethlisberger, Tom Brady and Cam Newton in the playoffs. This year, the pass defense has been even better: With a dominant pass rush, a back seven that doesn’t allow many completions, and a strong-tackling unit that limits gains, Denver’s allowing a minuscule 4.7 net yards per pass play. And while last year the pass defense allowed 19 touchdowns against just 14 interceptions, this year those numbers have flipped, with only six touchdowns against eight interceptions. By most measures, this pass defense is even better than last year’s. That’s a very scary fact for the other 31 teams in the league.