The Denver Broncos set numerous offensive records last year. The Chip Kelly Eagles had a fascinating offense that was lethal for stretches. The Saints offense was its usual efficient self, and the Chicago Bears under Marc Trestman had one of the best offensive years in franchise history.

Yet all of those teams had at least 61 drives last year that ended in a punt. San Diego , meanwhile, punted just 56 times. The Chargers only had 21 turnovers, which means only 77 San Diego drives could be clearly labeled as failures, or “bad drives.”

That’s pretty impressive; the 2013 Chargers were just the 36th team during the 16-game era to have fewer than 80 “bad drives” in a season. On the other hand, the Chargers were one of just five of those teams to score fewer than 400 points. San Diego’s offense was very efficient last year, but the 77 “bad drives” statistic is a bit misleading. That’s because the team had just 158 total drives last year according to Football Outsiders, while the average team had 186 drives.

Why did the Chargers have the fewest drives in the NFL? A bad defense certainly helped limit the team’s number of offensive drives: San Diego forced only 82 “bad drives” all year, too. But the main reason was that the offense was not just efficient, but uniquely efficient. According to Football Outsiders, San Diego averaged 3:22 per drive, a full 15 seconds more than the #2 team in that metric, Carolina. And the Panthers were the only other team to average at least three minutes per drive. One reason for the long time of possession is that the Chargers moved at a glacial pace between plays, rating as the 2nd slowest team according to Football Outsiders. The other teams in the bottom four in pace were all run-heavy — Carolina, Seattle, and San Francisco — which marks yet another way in which the Chargers were outliers. In several metrics — first downs per drive, yards per drive, and points per drive — San Diego and Denver were the top two teams in the NFL. But in pace, Denver ranked 4th, making the Broncos offense look and feel much different than San Diego’s attack.

Another reason the team’s average drive took so long to complete: San Diego averaged 6.85 plays per drive, with New Orleans second in that statistic with 6.35 plays. That’s because the Chargers had a very horizontal passing attack. According to NFLGSIS, Philip Rivers ranked 6th from the bottom in average length of pass at 7.75; only Jason Campbell, Sam Bradford, Matt Ryan, Alex Smith, and Chad Henne threw shorter passes. With the exception of Ryan, none of those quarterbacks came close, however, to matching Rivers’ league-leading completion percentage. What we have here is your classic hyper-efficient, short-area passing game, and the Chargers executed it beautifully.

In fact, here’s another unique part of the San Diego offense: it rarely targeted wide receivers. San Diego was one of just three teams to throw more passes to non-wide receivers than to wide receivers. Here’s how to read the table below: the Chargers threw 25% of all pass attempts to running back, 47.1% to wide receivers, and 27.7% to tight ends. Based on those percentages, San Diego ranked 4th in percentage of pass attempts to running backs, 30th in percentage of pass attempts to wide receivers, and 2nd in percentage to tight ends.

Tm RB WR TE RB % Rk WR % Rk TE % Rk NOR 32% 40.8% 27.6% 2 32 3 KAN 44% 41.1% 14.6% 1 31 31 SDG 25% 47.1% 27.7% 4 30 2 ATL 25% 54% 21.2% 6 29 15 STL 16% 54.5% 29.9% 25 28 1 HOU 19% 55.6% 25.3% 14 27 4 CLE 22% 56.7% 21.4% 8 26 12 OAK 28% 56.7% 15.5% 3 25 30 DET 25% 57.2% 17.7% 5 24 25 BUF 24% 57.6% 18.9% 7 23 22 SFO 16% 58.7% 24.9% 22 22 5 BAL 20% 59% 21.2% 11 21 14 CAR 16% 59.8% 24% 23 20 7 PHI 17% 60.3% 23.1% 20 19 8 DAL 15% 60.4% 24.4% 27 18 6 TAM 21% 61.2% 17.5% 9 17 26 NYJ 18% 61.6% 20.6% 18 16 17 IND 18% 62.3% 19.5% 16.5 15 19 DEN 17% 62.4% 21% 21 14 16 MIN 15% 62.7% 22.7% 28 13 10 CIN 14% 62.7% 23.1% 29 12 9 JAX 20% 63.2% 16.5% 10 11 29 SEA 16% 63.6% 20.5% 24 10 18 CHI 19% 63.7% 17.2% 13 9 27 ARI 18% 63.8% 18% 16.5 8 23 PIT 19% 64.2% 17% 15 7 28 NYG 18% 64.6% 17.8% 19 6 24 GNB 15% 65.3% 19.3% 26 5 20 NWE 20% 66% 14.3% 12 4 32 WAS 11% 66.7% 22.6% 32 3 11 TEN 14% 66.7% 19.3% 30 2 21 MIA 11% 67.9% 21.2% 31 1 13

Throwing shorter passes to the tight ends and running backs is one way to keep the chains moving, but you have to be extremely accurate if your offense consists of short passes. As it turns out, San Diego had the highest completion percentage in the NFL when throwing to running backs, the highest when throwing to wide receivers, and the eighth highest when throwing to tight ends:

Tm RB WR TE RB WR TE SDG 85% 65.3% 66.7% 1 1 8 DAL 82% 59.7% 66.7% 2 10 8 NOR 82% 64.3% 60.4% 3 4 24 TEN 81% 57.3% 66.3% 4 17 11 DEN 79% 64.7% 75.2% 5 3 1 SEA 79% 61.8% 65.2% 6 7 16 ATL 79% 63.9% 67.9% 7 5 5 PHI 78% 59.2% 62.8% 8 11 21 MIA 78% 57.3% 66.7% 9 18 8 CAR 78% 57.1% 66.1% 10 19 12 CHI 76% 61.7% 67.3% 11 8 6 CIN 76% 59.1% 66.4% 12 12 10 GNB 76% 65.1% 64% 12 2 20 BAL 75% 53.5% 60% 14 28 25 ARI 75% 58.7% 73.7% 15 13 2 BUF 74% 48.3% 64.9% 16 32 17 TAM 74% 50.2% 70.9% 17 30 4 IND 74% 56.7% 58.9% 18 22 27 STL 73% 53.8% 64.7% 19 27 19 DET 71% 54.1% 61.8% 20 26 23 WAS 70% 56.6% 62.2% 21 23 22 JAX 69% 56.8% 58.3% 22 21 30 PIT 69% 62.7% 71.1% 23 6 3 MIN 69% 57.3% 65.3% 2 16 15 KAN 69% 55.9% 65.5% 25 24 14 NWE 68% 60% 58.8% 26 9 28 OAK 67% 54.9% 57.7% 27 25 31 CLE 66% 49.7% 65.7% 28 31 13 HOU 65% 58.6% 58.6% 29 14 29 SFO 65% 57.8% 56.6% 30 15 32 NYJ 62% 51.4% 64.9% 31 29 17 NYG 59% 57.1% 59.6% 32 20 26

Mike McCoy and offensive coordinator Ken Whisenhunt brought a new offense to San Diego, but the Chargers new offense wasn’t just about the coaches. Rivers was pretty clearly helped by a couple of newcomers on the field, too. Danny Woodhead caught 87% of his targets last year, and ranked 1st in both DVOA and DYAR. The other was Keenan Allen, who had an incredible 68% catch rate (of the 12 receivers with at least 60 catches outside of the slot (according to Pro Football Focus), Allen posted the best catch rate. Are those marks sustainable? Is anything San Diego did sustainable last year?

My guess is probably not. San Diego was incredibly efficient in 2013, even if it was efficient in a way that did not capture the public’s eye. The Chargers had the fewest three-and-outs in the NFL, even on a per-drive basis. The team ranked third in first downs gained despite ranking last in possessions. The Chargers were masters of the short-passing game last year, and were also very effective in the running game (ranking 1st in percentage of stuffed runs and 5th in short-yardage running). That seemed even more true down the stretch. Ryan Mathews easily led the NFL in carries in December, and in those five games, Mike Scifres had just fourteen punts.

But something about San Diego’s success seems unsustainable to me, and I know that’s not a very convincing argument. On the other hand, I’m not necessarily predicting that the offense will struggle this year, just that it will look different. The return of Malcom Floyd, a deep threat who missed most of last year with an injury, should help open up the offense. The same goes for Ladarius Green, the number two tight end who looked like an explosive playmaker in just his second season. But the idea that San Diego will again lead the league in length of drive, plays per drive, operate at a glacial pace, and have the fewest bad drives in the NFL, all seems pretty unlikely.