Peyton Manning’s backup will make his first career start against the Bears—and against his old coaches who know his weaknesses. Look for Gary Kubiak to start installing the offense he always wanted in Denver

Whenever a young quarterback takes over for a veteran during the middle of the season, onlookers resort to platitudes in forecasting the young player’s chances. Maybe the new guy can provide a spark. Maybe he’ll inject some energy into the offense. Maybe he has the IT-factor. These, of course, are optimistic ways of saying absolutely nothing. The sentiments fail to consider that only twice this century has a quarterback who wasn’t a first-round pick replaced a veteran midseason and gone on to become a long-term star: sixth-rounder Tom Brady for Drew Bledsoe, in 2001, and undrafted Tony Romo for—coincidentally—Drew Bledsoe, in 2006. For every success story, there are untold scores of quarterbacks such as Andrew Walter—remember him?—that fall short of achieving even mediocrity.

Keep this in mind when you hear people talking about Brock Osweiler, who will start for the Broncos in place of an injured Peyton Manning this Sunday at Chicago. We know very little about the soon-to-be 25-year-old, but what we’ve seen so far isn’t particularly encouraging. It will be easy to expect too much from him because, at 6’ 7” and 240 pounds, he looks like a strong-armed pocket passer. You might even hear people comparing the 2012 second-round pick to Joe Flacco.

Flacco, however, is 6’ 6”. The minute difference in height is noteworthy because just five quarterbacks in NFL history have stood taller: Sonny Gibbs, Frank Patrick, Dan McGwire, Ryan Mallett and Osweiler. Given the countless men who have passed through the position, this can’t be a coincidence—just like it’s no coincidence that virtually no quarterback has been either abnormally short or astronomically fat. Most likely, being too tall can be a detriment to precision accuracy. This was certainly the case with Mallett, the most recent of the small-forward-sized QBs.

• BRONCOS PICK BROCK: Peter King examines the fall of Peyton Manning and Denver's decision to start Brock Osweiler against the Bears

Osweiler wasn’t the most accurate passer at Arizona State (60.6%). He often struggled with a low release point (a strange problem for a tall QB). More concerning, his arm strength didn’t (and still doesn’t) match his size. He pushes the ball instead of driving it. There’s little snap to his motion; his passes don’t fly with tremendous energy. This, along with so-so accuracy, was on display in Osweiler’s mop-up work against the Chiefs last Sunday.

In terms of throwing power, Osweiler is practically another version of this year’s Manning (though better than last week’s Manning, who completed just five of 20 passes for 35 yards and threw four interceptions). We can safely assume that, with all of 54 NFL passes on his résumé, Osweiler doesn’t have Manning’s sagacity when it comes to identifying throws well before they become open.

We’ve seen evidence of this, both last Sunday and in Osweiler’s limited reps last season. Instead of anticipating reads, he predetermines them, a common mistake made by young quarterbacks. This play last year at San Diego is such an example.

A few times against the Chiefs last weekend, Osweiler threw into safety help coverage when attacking the intermediate levels. When his first read was clearly defined, he was decisive. There were several productive short-intermediate throws just shy of the sticks, in front of Chiefs defenders who were giving a cushion while protecting a three-plus-score lead. When Osweiler had to work through his progressions, uncertainty set it. A great illustration came on Mike DeVito’s sack.

Remember, these plays—all of Osweiler’s NFL snaps, actually—have been taken with him coming off the bench. That means he was operating a game plan designed for Manning, was often playing when the score was out of hand, and was coming off a week where he did significantly more observing than practicing. Perhaps Osweiler is a totally different quarterback when things are tailored for him. But let’s assume that Osweiler is exactly what we’ve seen so far heading into Sunday’s game against the Bears. The question then becomes, How will the Broncos play with the guy?

All season there has been a tug-of-war in Denver over whose offensive system prevails: head coach Gary Kubiak’s or Manning’s? Osweiler, of course, has no system; it reasons that Kubiak will install a few more of his preferred zone concepts, both in the running game and in the moving-pocket play-action game that we saw when Kubiak coached the Texans. Osweiler isn’t mobile, but unlike Manning, he’s not immobile either. Physically, Osweiler can run the full gauntlet of Kubiak’s stretch-zone game.

But with Manning at the helm, we haven’t seen a lot of stretch zone-action from Denver. It’s an offensive style that needs to be routinely practiced with diligence. A true outside zone attack isn’t something you just drop into a game plan. If it were, every team would do that because, when executed properly, it’s a highly effective approach.

The Broncos, most likely, have at least drilled some of these items regularly under Kubiak. After all, the team’s original plan was for this to be Kubiak’s full system and very little of Manning’s. (Things have played out differently.) But this offense won’t turn into the Houston Broncos. And it remains to be seen whether Denver’s perpetually shuffling O-line has the athleticism and the continuity to consistently run stretch zone.

On the plus side, the Broncos probably have the right skill-players to expand the zone scheme. Running back Ronnie Hillman is quick and C.J. Anderson plays with the center of balance needed for strong one-cuts. On the receiving side, tight end Owen Daniels has spent his career in this scheme under Kubiak with the Texans and Ravens, while wideouts Demaryius Thomas and Emmanuel Sanders are proficient on crossing patterns. We’ve already seen many variations of these concepts in Denver’s system with Manning, both this year and in previous years under coordinator Adam Gase, who is now coordinating Chicago’s offense.

The zone scheme would put Osweiler on the move. The beauty is that the types of throws that blossom here don’t require great arm strength. Kubiak, you might recall, had a lot of success coaching Matt Schaub. When you move the quarterback or the pocket, the field effectively slices in half. (Quarterbacks don’t throw back across the field, away from their rollout, unless it’s a designed throw against the grain.) Thus, there are fewer reads and simpler either/or decisions to sort through. This can be especially helpful for a quarterback whose first NFL start is coming on the road against his former coach. John Fox is one of the few people in the league who is familiar with the specifics of Osweiler’s weaknesses. You can bet Fox and defensive coordinator Vic Fangio will confer with Gase (Osweiler’s former position coach) and gather the exact schematic wrinkles that Osweiler will least want to see.

The simpler the reads in Denver’s game plan, the less vulnerable Osweiler will be. That said, not every drop-back can feature moving pockets—especially since the offense hasn’t extensively practiced for that this season. As is the case in every NFL game, Osweiler will find himself in third-and-long situations, which demand crisp throws from a crowded pocket. Expect the Broncos to rely on the shorter catch-and-run type throws they’ve already built much of their passing game around. Since they’re facing a Bears’ defense that is predominantly zone-based, those will actually be catch-and-sit throws in the coverage’s natural holes. It will be important to use spread formations that space out the defenders, which will clarify the reads so Osweiler can better anticipate the voids.

However this forced experiment goes, one thing is clear: if the Broncos are to remain Super Bowl contenders in 2015, they must continue to rely heavily on their defense.

• Question? Comment? Take it up with Andy Benoit on Twitter.