Entering 2013, Northwestern had high expectations, with a preseason ranking and serious talk about NU's potential to contend for a conference title. The offense's hopes were pinned on three players: quarterbacks Kain Colter and Trevor Siemian, and running back Venric Mark.
Almost immediately, the plan went off track: Kain Colter started the season opener at Cal by hitting Dan Vitale for a 23 yard gain, then left the game with an injury suffered on the next play. He would not return to the game, and the rest of the season would see him in and out of the lineup while battling injury.
Filling in for Colter, Trevor Siemian opened the season with a 18-29, 276 yard, 1 TD, and 2 INT performance, while leading Northwestern to a 44-30 win. Siemian's passing, however, was a minor story from a game that also saw Venric Mark leave with an injury and Colin Ellis provide the winning margin with a pair of defensive scores; even with Siemian's strong day through the air, the offense had frequently sputtered against an awful defense.
From the first game, Northwestern's offense was derailed by injury. Mark would return against Ohio State before an injury against Wisconsin finished his season with only 97 yards on 31 carries. Colter was able to fight through his injuries, only missing the Minnesota and Illinois games completely, but his role was diminished in several other games and his productivity dropped across the board. Eventually, it came out that Siemian, who appeared in every game, also struggled with injuries down the stretch.
During the nonconference schedule, things went fairly well: NU moved the ball at will against Syracuse in week 2, racking up 581 yards and 48 points, with both quarterbacks performing well. The next week, a slow start against Western Michigan (Northwestern trailed 10-7 midway through the second quarter) was a worrying sign, but NU broke through on the ground, piling up 332 rushing yards and 38 points against a mostly hapless MAC opponent.
The first serious sign of trouble came against Maine. Siemian struggled, managing only 5-8 passing for 37 yards, with another 11 yards on his two carries. Colter posted a somewhat better statline, completing 5 of 9 passes for 85 yards and a touchdown, though he also threw an interception. Colter also added 38 rushing yards and a touchdown on 12 carries. The running game took up some of the slack, as Northwestern rushed for 251 yards on 49 carries, with Mike Trumpy having his best game of the season.
On a lackluster day for the quarterbacks, the defense once again chipped in the winning margin, scoring two touchdowns on the way to a 35-21 win. Against an FCS opponent, even a fairly good one, this was not an encouraging sign.
Entering conference play, Northwestern was 4-0, winning every game by at least 14. On the other hand, the defense had scored 4 touchdowns, an unsustainable rate to say the least, and the offense had experienced significant struggles against 3 of 4 opponents, including a truly awful Cal defense and FCS Maine. The issues were particularly glaring in the passing game, which followed a torrid start against Cal and Syracuse (49 of 67 for 674 yards, 5 touchdowns, and 2 interceptions) with troubling games against Western Michigan and Maine (25 of 39, 261 yards, 2 TDs, 2 INTs). Treyvon Green ran hard in relief of Venric Mark, averaging over 100 yards per game and scoring 5 touchdowns out of conference, but he was unable to carry the offense when the quarterbacks slowed down.
Then came the Ohio State game, which seemed to answer Northwestern's offensive questions: even while a fierce OSU run defense held the Cats to 94 yards on the ground (helped by an equally tough pass rush), Trevor Siemian passed for 245 yards at 13.6 yards per attempt (13-18), while Kain Colter added a perfect 12-12 for 98 yards. OSU managed the win, with a freak defensive touchdown on the final play stretching the score to a comfortable-looking 40-30, but Northwestern had taken the top team in the conference to the wire, mostly on the strength of a pair of strong passing performances. It was the last time the 2013 offense would look threatening.
After Ohio State, things fell apart completely: Kain Colter was injured early against Wisconsin, and Northwestern barely moved the ball in a 35-6 loss. The next week, Trevor Siemian, playing through an injury of his own, threw a crucial pick-6 in a 20-17 loss to Minnesota, who stifled the running game and held Siemian to a poor 5.1 yards per attempt.
After Minnesota, Northwestern repeatedly fell short in low-scoring games: losing 17-10 in overtime to Iowa, then 27-24 to Nebraska on a Hail Mary, then 27-19 in triple overtime (it was 9-9 at the end of regulation) to Michigan. This stretch saw the quarterbacks combine for 2 touchdowns and 4 interceptions, while the team's yards per attempt ranged between an awful 3.9 against Nebraska to a somewhat respectable 7.4 against Iowa.
By the end of this streak, a 30-6 drubbing by Michigan State was almost a relief from the heartbreak; the offense once again struggled, but that was expected against the Spartan defense. A narrow win over Illinois prevented a winless conference season, as the Wildcats limped to a 5-7 finish.
The role of injuries in determining who could play and how much limits the conclusions that can be drawn about the quarterback platoon; Colter, in particular, missed two games completely and was able to provide a limited contribution in several more games. Statistically, both quarterbacks improved their yards per attempt from the previous year (for Siemian and Colter respectively, from 6.0 and 5.8 to 7.2 and 7.1). Interceptions were up, from 7 to 13, though still not to an exceptional level overall.
Two statistics point to the offense's overall problems. First, Colter's rushing output dropped from 891 yards at 5.27 yards per carry to 489 yards at 4.25; combined with difficulty keeping running backs on the field, the steady running game that had carried the 2013 offense was gone. The second comes from S&P+. Interestingly, this measure puts Northwestern at a mediocre 52nd overall (49th rushing, 35th passing). On passing down (second and third downs with long yardage to go), Northwestern dropped to 80th. Overall, Northwestern was not an awful offense; when they ended up off schedule, however, they struggled to get back on track, while the running game that could reliably gain yardage on early downs the year before failed to show up in many games.
After emerging as an improvised solution to quarterback injuries in 2010 and 2011, the two-quarterback system was an established principle of the offense by 2013. Unfortunately, we never got to see it working at full effectiveness, as injuries dictated playing time for much of the season. Furthermore, a significant decline in the running game put more pressure on the quarterbacks to deliver through the air; the modest gains in passing efficiency they delivered were not enough to make up for more turnovers and a lack of consistent gains on the ground.
Going into 2014, Northwestern plans to abandon the quarterback rotation. While potentially useful, it was at its most effective when Colter and Siemian's skillsets could provide radically different threats; there is no such contrast in styles on the current roster. For a team that wants to be able both to use option concepts to run the ball and to throw downfield, however, the possibility of using a rotation to open up these two parts of the offense rather than looking for a dual threat who can handle both is worth keeping in mind for the moment when the roster looks right.