This quote comes from Tom Coughlin in a recent NY Times article (registration required):
I'm a believer that defense wins championships, ... And I'm a believer that you have to be able to have great defense, and you've got to be able to run the ball and stop the run."
I have heard the "defense wins championships" mantra probably more than any piece of sports "wisdom." The rush defense is a common corollary. With the NFL playoffs approaching, the "defense wins" gong will only ring louder. The NY Times writer adds some backup,
Rush defense is a strong barometer of championship potential. More than three-quarters of Super Bowl teams had a top-10 rush defense, according to the Elias Sports Bureau. Nine of the past 14 participants were in the top five ...
So far this season, teams with a top-10 run-stuffing defense have 7-5 records or better.
On closer inspection, the "evidence" provided might come closer to supporting a proposition stating that being better than average rush defense often goes along with winning.
Over the years, I heard "defense wins championships" so much that in From the Ballfield to the Boardroom, I decided to collect a bit of evidence in a section about separating fact from folklore. The data covered 1970-2000 and lends some bit of credence to the mantra for the decade of the 1970s, where the AFC dominated and the median AFC champ ranked first in defense. Since the 1970s, a more accurate statement is: "Teams with solid offenses and solid defenses win championships." Such a statement seems self-evident but does offer a counterpoint to the deafening cliche about defense.
Over 1970-2000, only 10 of 31 Super Bowl winners had higher ranked defenses than offenses. Only 22 of 62 AFC and NFC champions had higher ranked defenses than offenses. Since 1970, of the top ten teams allowing the fewest points as a percent of that year's median, only 3 won or even made the Super Bowl ('75 Steelers, '85 Bears, '00 Ravens). Four of the top ten did not even make the conference championship game. On the other side of the coin, 6 of the top 10 offenses in terms of points relative to median points in a year won the Super Bowl, 7 made the Super Bowl, and all but one made the conference championship.
Since 1980, only the Ravens could really be described as winning the championship with great defense and mediocre offense. The 1985 Bears, while great on defense, also led the league on offense. Some might offer a rebuttal based on great defenses helping to make offenses more productive, but the same holds true for offenses helping defenses.