The first thing an offense has to decide is who to put on the field and where to put them. Unfortunately, this is also a place where I don't have much information to work with and where this year's approach is likely to change dramatically from the last couple of years. I can still say a few things after the jump.
The offense lists 12 positions on the depth chart: the five offensive line positions, four receiver positions, quarterback, superback, and tailback. Obviously, the offense can only have eleven players on each play; furthermore, while superbacks are supposed to be able to fill several roles, those snaps are frequently divided according to formation. Last year, three receivers, one superback, and one tailback served as the base personnel group, with Drake Dunsmore frequently lining up in all three of the tight end, h-back, and slot receiver positions. Three substitutions were common: replacing the superback with a fourth wide receiver, replacing the tailback with a fourth receiver (either as an empty backfield or using the superback as a blocker), and replacing the superback with a second running back. Unfortunately I don't have charting that would indicate how common each of these were, but the outline is accurate. I don't know if Northwestern took a single snap with five true receivers on the field. Goalline/short yardage packages were an exception to the outline, using more traditional personnel (read: runningbacks/superbacks everywhere).
This year, I would expect the personnel mix to change due to Dunsmore's departure. Unless one of the superbacks steps up in a big way, I would expect his snaps to be split between the fourth receiver position and at least one (and possibly more than one) superback. Otherwise, I have no predictions about what will change this year.
When you say "spread offense," most people think of a formation like this:
Move the back into the pistol and nothing much changes:
Northwestern used at least three personnel packages for these balanced, four-wide formations: three receivers and a tailback were almost universal, but the second slot receiver could be a wide receiver, superback, or tailback. A balanced formation with a tight end or h-back presents a similar threat to the defense, with a bit more versatility in pass protection and run blocking traded for a slower release as a receiver. In either case, these formations can easily threaten any part of the field with multiple receiver pass concepts while presenting a balanced run threat.
The other classic spread formation is the four receiver trips formation that you get by putting both slot receivers on the same side of the field. You get a similar stress on the defense by putting a tight end/h-back on the same side as two receivers as shown below:
This formation obviously presents an unbalanced threat to the defense, requiring an adjustment to match the three receivers threatening the left side. This type of formation is frequently used to isolate the single receiver by drawing the defense's numbers to the front side to deal with the obvious threat of three-receiver concepts. A strong adjustment to the three-receiver side might also leave the offense with a numbers advantage running the ball, especially if the defense is unwilling to leave a one-on-one matchup to the single receiver side.
The other common formations last season were also unbalanced. First, an empty backfield:
If memory serves, Northwestern never used a quads formation, so three-by-two is the only relevant formation here except the variation trotted out in the bowl game, with a tight end and an h-back:
The top formation is (obviously) mostly a passing formation. It severely limits pass protection, but if the line and quarterback can be trusted to handle the rush it is unmatched for quick passes. Success with those passes (or screens, though receiver screens were not a significant part of the offense last year) can compel the defense to limit the blitzes that can overwhelm five man protection. The bottom formation was mostly (indeed, I believe exclusively) used to run Colter. I would be surprised if it became a major part of the offense this year.
The last group of formations commonly used were three receiver, two back formations, either with the backs split:
or as a sort of pistol variant on the offset-I:
These formations are best suited to runs and deep passes, as the running backs are well positioned for blocking and poorly positioned to catch passes. The pistol variant is perhaps better suited to using a lead blocker and the shotgun to triple option plays, but they are broadly similar in their strengths and weaknesses.
Outside of goal line and short yardage situations, Northwestern stuck to these formations for the vast majority of snaps last season. Motion was mostly used to move between these formations. I would expect no major changes to the formations this year, only normal offseason tweaks and adjustments for personnel.
Bill Connelly is previewing every FBS team this year, and as part of his statistical breakdown he offers an overview of the offense's tendencies in 2011. There is nothing surprising here: Northwestern was just barely on the run-heavy side of the FBS, running 61.9% of the time on "Standard Downs" (versus an average of 60.0%) and 33.6% on "Passing Downs" (against an average of 33.3%). In the red zone, the Cats were notably run heavy, running on 70.9% of plays compared to an average of 60.4%.
In simple run/pass terms, I expect more running this season for three reasons. First, Colter taking over as the full time starter means that the option runs that weren't viable for Persa last season should be a more important part of the offense. Second, I expect pass protection to be atrocious and run blocking to be serviceable. Third, I expect Colter to use his legs a fair amount on called passes. Situationally, the Persa pass/Colter run tendency is gone unless a quarterback platoon reappears. More running overall likely mans at least as much in the red zone.
The safest prediction about Northwestern's tendencies is probably that the offense will continue to operate at a fast pace. This is likely both because NU has been doing this since Randy Walker introduced the spread offense and because a team with inferior depth ought to get some advantage from limiting substitutions. Since, unfortunately, Northwestern is definitely not one of the most talented teams in the Big 10, we will have to hope that any slight schematic advantages pay off.