The Arizona Cardinals are 8-1, giving them the best record in football. The Detroit Lions are 7-2, tied with the Patriots and Broncos for the second-best record through ten weeks. ^[1]The Eagles can match that record tonight with a win against the Panthers. In week 11, the Lions head to Arizona in a game that may well decide which team gets home field advantage in the NFC playoffs: it certainly will decide which franchise is in the pole position with five weeks left.

We should be celebrating these teams. Detroit has only had one year in its last 70 seasons when it started with a better record through 9 games: that was the ’54 squad, which began 8-1 and finished with the Lions in the NFL title game. Detroit also started 7-2 in 1993: that’s the only other time in the last 50 years that the Lions have started so well through nine games.

For Arizona, the situation is even bleaker. The team has won at least 8 of its first 9 games just two times before this year. One was in 1948, back when Hall of Famer Jimmy Conzelman  was coaching the team (then in Chicago). And the other was in 1925, when Chicago was led by Hall of Famer Paddy Driscoll. That’s it. The oldest franchise in NFL history has started with an 8-1 record (it has never began 9-0) now just three times. On the first two occasions, the Cardinals wound up winning the title, albeit with one asterisk.

But both the Lions and Cardinals have been overachieving this year, at least according to their Pythagenpat Records. Detroit has scored 182 points and allowed 142 points; that gives the Lions a 0.648 Pythagenpat winning percentage. Among the 72 teams to start 7-2 between 1990 and 2013, 59 had better Pythagenpat winning percentages.

In that group, 39 of those teams had Pythagenpat winning percentages of at least .700; they won, on average, 3.9 of their next 6 games. ^[2]I have excluded week 17 for purposes of this study, since many of these teams will have had nothing to play for. The other 33 teams won just 3.2 of their next six, proving once again that Pythagenpat records do have predictive ability. The Lions are a very good team, and one that has excelled without Calvin Johnson for long stretches. A 0.648 Pythagenpat winning percentage translate to 10.36 wins out of 16, so the Lions are no fraud. But a 7-2 record overstates things quite a bit. ^[3]On the other hand, Detroit’s true win percentage is 0.625.

For Arizona, the situation is much more severe. The Cardinals have scored 223 points and allowed 170. That translates to just a 0.668 Pythagenpat winning percentage. That’s easily the worst of any team since 1990 to start 8-1 or 9-0. Here’s how to read the table below: In 2007, the Patriots won 9 of the team’s first 9 games, scoring 355 points and allowing 147 in the process. That gave New England a 0.918 Pythagenpat winning percentage. The Patriots finished the year with 16 wins.

The good news for the Cardinals is that all of those teams won at least 11 games and made the playoffs. However, that 0.668 Pythagenpat Win percentage is the worst of any team since 1990. ^[4]Imagine how things would look if Patrick Peterson and Antonio Cromartie didn’t score late touchdowns against the Rams yesterday! In fact, of the 134 teams since 1920 to win at least 8 of 9 to start the year, Arizona ranks 132nd in Pythagenpat winning percentage through 9 games. The only two worse teams? The 1987 Chargers and 1976 Raiders.

San Diego lost its first game that year, won some close games with replacement players, and kept that tradition alive when the real players returned. Then, after an 8-1 start, the team lost its final 6 games. Those were the final six starts of Dan Fouts’ career.

The 1976 Raiders went the other way. It was one of the weirdest seasons in NFL history. Despite a 13-1 record and a Super Bowl title, Oakland was a pretty average team through nine weeks, outscoring opponents by just eleven points! Of course, a 48-17 blowout in New England skewed things a bit, but Oakland was not a great team (particularly on defense) by Super Bowl champion standards (despite the lofty record).

Of course, there’s a limit to how much history can tell us. This is fun to look at, but both teams can change their level of play significantly over the last seven weeks. Despite what appears to be a very “over-achieving” start, if the Cardinals falter, much of the blame will likely be assigned to new quarterback Drew Stanton. He’ll be starting, of course, because Carson Palmer appeared to suffer a season-ending leg injury against the Rams. Even when things go well for the Lions and Cardinals, it seems like the other shoe won’t wait long to drop.