A month into its season, Notre Dame couldn't have asked for a better start. A 4-0 record and No. 9 ranking in the AP poll represent the program's best beginning to a season in a decade, and that success is the product of two big-picture keys: Fewer turnovers by the offense, and suffocating play by the defense.
Breaking that down a little further, here are six numbers to know about Notre Dame through four games:
4: Number of big (30 yards) plays allowed
Only three FBS teams have allowed fewer explosive plays than Notre Dame, and only one of those defenses -- Florida -- has done it against an equally difficult schedule. The Irish defense has allowed three plays of 30-39 yards and only one play for over 40, so it's no surprise Notre Dame is allowing just 0.15 points per play, the sixth-best average among FBS programs.
2: Red zone touchdowns allowed
Keeping in mind Notre Dame's ability to limit big plays, the defense's ability to limit red zone touchdowns stands out even more. Irish opponents have reached the red zone 10 times, scoring just a pair of touchdowns and kicking four field goals. This is a defense that plays well between the 20s, but buckles down in the red zone. Only TCU has allowed fewer red zone touchdowns this year (1).
9: Average points allowed
Only Alabama (7) and TCU (7.3) have averaged fewer points allowed, and both those teams haven't faced the kind of schedule Notre Dame has. Regardless, though, Alabama has the best defense in the country, but Notre Dame's firmly in the next tier below the Tide.
13: Turnovers forced
Last year, Notre Dame's defense recovered six fumbles and intercepted eight passes in 12 games. Through four games in 2012, the Irish defense has recovered five fumbles and intercepted eight passes, with five of those interceptions coming against Michigan Sept. 22.
Statistically speaking, Notre Dame has been lucky in terms of generating interceptions. College football stat guru Bill Connelly's research shows about 21.9 percent of passes defended (passes broken up interceptions) are picked off; Notre Dame has defended 21 passes and picked off 8 for a rate of 38 percent.
But it's not all luck that's led to those interceptions -- the strong play of Notre Dame's front seven has led to plenty of hurried or forced throws from opposing quarterbacks, leading to that high interception rate. Instead, it's a combination of Notre Dame getting a little lucky, but also making a lot of their luck through its pass rush.
4: Turnovers committed
And here's the biggest reason why Notre Dame is 4-0: Notre Dame turned the ball over 15 times through four games in 2012 en route to a 2-2 record, but over the same span this year the Irish have a 9 turnover margin.
"My wife even talks to me when I'm plus 9," coach Brian Kelly joked after the Michigan game, "which didn't happen much last year."
28: S&P ranking for Notre Dame's offense
In a nutshell, S&P (via Football Outsiders) measures the success and explosiveness of every play an offense runs or a defense faces. It's a pretty good catch-all that's adjusted for strength of schedule, and Notre Dame's offense actually rates pretty well by it.
Nobody's mistaking Notre Dame's offense for Geno Smith's outrageous West Virginia attack. But thanks to a solid run game headlined by Theo Riddick, Cierre Wood and George Atkinson III, the Irish offense can hold its own, especially given how few turnovers it's committed.
The S&P metric gives a lot of credit to Notre Dame's tough schedule, as their unadjusted numbers rank 76th in the country. Consider, too, that Notre Dame's doing it with a freshman quarterback who hasn't been able to ease into anything.
In short: Notre Dame's offense may not be as bad as it seems. That's the good news. The bad news, though, is Notre Dame's schedule doesn't ease up until early November, so chances are they'll be locked in plenty of close defensive battles as the season progresses.