Repeating as Super Bowl champion is tough.

However, the step backward that the Ravens took in 2013 was worrisome. According to nERD, one of our signature metrics, the Ravens were just the 23rd-best team last year. Their nERD score in 2013 was -2.90, meaning they'd be expected to lose to an average team on a neutral field by about a field goal.

This year? Their nERD improved to 5.53 by the regular season's end, fifth-best in the league. How did they do it?

Let's dig into the numbers and find out.

The Good

Joe Flacco was good this year, according to our Net Expected Points (NEP) metric. NEP indicates how well above or below expectation a player performs. It's weighted on situational results, which means that a 10-yard pass to pick up a first down and a 10-yard pass on third and 15 aren't weighted the same because one adds to a drive and to a drive's expected point outcome and the other doesn't.

Last year, Flacco posted a Passing NEP of -18.84, which ranked 28th out of 39 quarterbacks with at least 200 drop backs. His Passing NEP per drop back was -0.03, 27th-best. This year, his Passing NEP was 89.35, which ranked 10th out of 37 qualified quarterbacks, and his per-drop back Passing NEP of 0.16 was 11th.

Now there's an eye-opener and no mistake.

Flacco's improved play was either a result of or resulted in solid seasons from both Steve Smith and Torrey Smith, both of whom ranked inside the top 25 in Reception NEP among receivers (22nd and 25th, respectively).

The Ravens, who had the seventh-best overall offense in the NFL, also had a big improvement at running back. Last year, the Ravens posted an Adjusted Rushing NEP per play of -0.12. This year, it was 0.01. Much of this was because of Justin Forsett's production behind the offensive line. Forsett was second among running backs in Rushing NEP (22.67).

On a per-play basis, Baltimore also had the fifth-best defense and the second-best rushing defense when adjusted for schedule.

For the fifth-best team in the league, there weren't many weaknesses. But, of course, there was a rather noticeable one in Baltimore this year.

The Bad

Passing defense.

Really though, the secondary -- all things considered -- wasn't that bad. They allowed just 22 passing touchdowns this year, tied for sixth-fewest in the NFL. They lacked turnovers, though. The Ravens totaled just 11 interceptions, tied for 25th in the league.

As for the metrics, the Ravens posted an Adjusted Defensive Passing NEP per play of 0.08, which ranked 17th in the league and was the only facet of their game that ranked outside the top 12.

Justin Tucker, now a free agent, also had his worst season as a pro. He converted on just 85.3 percent of his field goal attempts (29 of 34), down from 92.7 percent (38 of 41 last year). His Field Goal NEP this year was just 26.18, down from 40.41 in 2013. This year, Tucker ranked 10th in Field Goal NEP. Last year, he had the highest mark among all kickers. Entering the season, Tucker was 10 of 11 (90.9 percent) on field goals 50 yards or longer. This year, he was just 4 of 9 (44.4 percent).

Moving Forward

The Ravens had a huge improvement in overall offense, jumping from 27th to eighth in Adjusted NEP this year. They had top-10 rushing and passing offensive units, and with their top-tier rush defense, they were once again one of the best teams in the NFL.

In order to keep the offense intact, the Ravens will need to re-sign Torrey Smith and Forsett, both of whom are free agents in 2015. Owen Daniels, who ranked 12th in Reception NEP per target (0.63) among 27 tight ends with at least 50 targets, is also a free agent.

On the defensive side of things, safeties Will Hill and Darian Stewart are also unrestricted free agents.

The on-field product in Baltimore was among the best in the NFL this year. Figuring out how to improve the secondary -- and trying to retain key offensive pieces -- will be key for the Ravens as they move forward to the 2015 season.