Tom Brady is the first quarterback in NFL history to lose a game after throwing for at least 500 passing yards, three touchdowns and no interceptions. (Jeff Roberson/Associated Press)

The New England Patriots have been an NFL powerhouse over the past two decades. But Sunday’s Super Bowl LII loss to the Philadelphia Eagles raised some red flags about their future, and Coach Bill Belichick and the front office will have significant concerns to address in the offseason, none bigger than their quarterback succession plan.

Yes, Tom Brady said before the game that he would return for the 2018 season, but as well as he played at 40, he can’t play forever. And that stellar play is precisely the reason the Patriots should be so concerned — because Brady has been covering up a lot of warts.

Think about this for a second: Brady threw for 505 yards, three touchdowns and no interceptions for a 115.4 passer rating, yet found himself on the losing end. Before that performance, the Patriots were 5-1 when Brady threw for at least 400 yards, two touchdowns and no interceptions. They had been 69-1 in starts when Brady’s passer rating was 115 or better, the lone loss at the hands of Peyton Manning and the Indianapolis Colts in Week 9 of 2005.

The question becomes what the Patriots will look like with a quarterback not named Brady under center — particularly after they parted with backup Jimmy Garoppolo in a trade during the season. A dip from Brady to an average quarterback could carry considerable consequences.

Brady turns 41 in August, and it’s fair to expect his performance to start to dip. Since the merger in 1970, there have been three quarterbacks to throw at least 200 passes in a season at 41 or older. Warren Moon did it in 1997 and 1998, and Vinny Testaverde (2004) and Brett Favre (2010) did it once. If we lower the bar to 100 passing attempts at 41 or older, we can add two more seasons from Testaverde (2005 and 2007), plus a year of Doug Flutie (2003).

Quarterback Year Age GS Cmp Att Cmp% Yds TD Int Rate
Warren Moon 1997 41 14 313 528 59% 3,678 25 16 83.7
Vinny Testaverde 2004 41 15 297 495 60% 3,532 17 20 76.4
Brett Favre 2010 41 13 217 358 61% 2,509 11 19 69.9
Warren Moon 1998 42 10 145 258 56% 1,632 11 8 76.6
Vinny Testaverde 2007 44 6 94 172 55% 952 5 6 65.8
Doug Flutie 2003 41 5 91 167 54% 1,097 9 4 82.8
Vinny Testaverde 2005 42 4 60 106 57% 777 1 6 59.4

If Brady were to regress quickly, before the Patriots can install a suitable backup, the franchise could falter. Brian Hoyer, who finished the season as Brady’s backup, has a career 83.3 passer rating, which would be considered below-average performance since 2012. Odds are that Hoyer will not be Brady’s successor. Still, the Patriots have to find a quarterback who is better than average if they want to maintain their status as perennial favorites to win the AFC East and challenge for the Super Bowl. That could be tricky, at least in the short term.

Since 2002, there have been just five rookie quarterbacks who have thrown at least 300 passes in their first year while also maintaining an above-average passer rating: Dak Prescott, Marcus Mariota, Robert Griffin III, Russell Wilson and Matt Ryan. Just 26 passers out of 69 (37.7 percent) who have changed teams since 2002 — via trade or free agency — have both qualified for the passer rating title and produced an above-average passer rating for their new team in their first season.

Even a fall back to average quarterback production or worse could be extremely problematic. The collective record of below-average quarterbacks (by passer rating) is 1,289-1,787 since 2002 for a winning percentage of .393, equaling a 6-10 record over a 16-game season.

Dubbed the “Mother of All Stats” during the 2012 Pro Football Researchers Association biennial meeting, net passer rating during the regular season has been a litmus test for Super Bowl-caliber teams. Since 2002, 23 of the past 32 Super Bowl participants, including 11 of the past 16 winners, had a net passer rating differential among the top five in the league. The Eagles just made the cut at No. 5 (plus-18.1), while the Patriots finished at No. 10 (plus-13.1) after an MVP-caliber performance by Brady (102.8 passer rating, third-highest in 2017). Sub in average passer performance (or worse), and New England’s championship potential looks even worse.

2017 New England Patriots Net passer rating NFL rank
Tom Brady’s performance plus-13.1 10th
Average performance minus-4.2 18th

As constructed, so much of New England’s offense flows through its passing game. Through the lens of expected points added — the difference between how many points per game an offense scores compared with what we would expect after taking into account down, distance and field position — in 2017, Brady and his receivers added a league-high 7.3 more points per game than expected. The rest of the league managed just 0.6 added points per game. Since 2001, Brady’s first year as a starter, no passing offense has been more prolific. Offenses led by league average quarterbacks were significantly less successful.

Not only would the Patriots’ offense take a huge step back if Brady fails to maintain his MVP-caliber performance, the surrounding cast could change significantly, too. Dion Lewis (the third-best rusher per Pro Football Focus in 2017) and Rex Burkhead, wide receiver Danny Amendola (the second-best receiver in the playoffs, per PFF) and left tackle Nate Solder are all free agents. Plus, Pro Bowl tight end Rob Gronkowski has said his future with the team is uncertain.

Maybe Gronkowski does return, and the organization finds other players to step up and make plays. But the more likely scenario is we just witnessed the beginning of the end of the Belichick/Brady era. Eventually, Father Time is going to catch up with Brady. And when he does, it could bring some rare down years in New England.

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