A common adage in football goes like this: if a team has two quarterbacks, it has none.

This suggests that any team who feels compelled to give game snaps to more than one signal-caller lacks a player worth taking all the reps. Case in point: the Steelers never removed Ben Roethlisberger from the field in favor of his backup. There was never a time where they said, “let’s take out Ben and play our change-of-pace guy.” Roethlisberger was good enough in his own right to make that change-of-pace guy extraneous.

Similarly, the Patriots never subbed out Tom Brady for their so-called “dual threat” quarterback. The Chiefs don’t take out Patrick Mahomes for similar reasons. You get the picture. When you have a stud, you ride the stud. That’s the way it goes.

Which brings us to the current quarterback situation in Pittsburgh. Russell Wilson has been the starter for the past five weeks, during which the Steelers have gone 4-1 and averaged a respectable 25.6 points and 363 yards per game. Wilson has thrown seven touchdowns against just two interceptions over that time, has completed 63.1% of his passes and has a quarterback rating of 98.6. Should that rating hold, it would be the best by a Steelers quarterback since Roethlisberger posted a 103.3 in 2014.

Why, then, has offensive coordinator Arthur Smith inserted backup Justin Fields into the lineup at times the past two weeks? Fields, who piloted the Steelers to a 4-2 record over the first six weeks before Wilson replaced him, hasn’t taken a significant number of reps – he took three against Baltimore and seven against Cleveland – but those reps have come in big moments. Fields quarterbacked the final two plays of the Baltimore game, helping to produce a first down that allowed the Steelers to run out the clock and secure a two-point win. And he was on the field for a fourth down play against the Browns as well as a couple of late snaps in a three-and-out possession that preceded Cleveland’s game-winning touchdown drive.

Obviously, the Steelers view Fields as a gifted athlete whose ability to make explosive plays benefits the offense. Fields has run the ball five times the past two weeks for 43 total yards, an average of 8.6 yards per carry. That type of production makes him dangerous.

It hasn’t been perfect, however. Fields was stuffed on that 4th-and-2 snap against Cleveland on a play he either misread or simply took too long to develop; and, he failed to connect on a deep throw to George Pickens on 3rd-and-4 with just over three minutes left, giving the Browns the ball back in time to author their game-winning score.

Fields recently told Ray Fittipaldo of the Pittsburgh Post-Gazette that he has a set package of plays each week, and that Smith has expressed an interest in using the package more frequently. I think most Steelers fans like the idea of inserting Fields into the lineup to put his athleticism to use. But when should Smith play Fields, and what should he run when Fields is out there? There is no consensus on this sort of thing because few teams attempt it. Again, most like to settle on a single quarterback for the sake of continuity. And, in most situations, the separation between the starting quarterback and the backup is significant.

Therein lies the rub for the Steelers. How wide is the separation between Wilson and Fields? Wilson is a better passer, no doubt about it. He can make throws Fields cannot, and he sees the field in a way that allows more of the team’s receivers to become involved in the offense. He is particularly adept at pushing the ball down the field. His 8.1 yards per attempt this season is far better than Fields’s average of 6.7. Wilson can scramble and extend plays, too, not on an elite level like he once did but at least functionally.

Fields, though, presents capabilities Wilson does not. Fields’s ability as a runner allows Smith to devise plays that integrate an extra blocker into the scheme because the quarterback is not simply handing the ball off and then watching the play. That alone makes defenses accountable in a way they are not when Wilson is on the field. And, while not on the same level as Wilson as a passer, Fields has shown himself capable in that area. His 65.8 completion percentage and 5:1 touchdown-to-interception ratio this season are both slightly better than what Wilson has authored.

So far, Smith’s use of Fields as the “changeup” quarterback has centered on his running ability. Eventually, defenses will catch on to this and will overplay the run when Fields enters the huddle. If Smith intends to use Fields more frequently, as Fittipaldo suggested, the key will be to find the right passing package to exploit this tendency.

However, the more Smith expands his use of Fields, the less he’s playing Wilson. This is great if both quarterbacks are on board with the plan. But with neither Wilson nor Fields signed beyond this season, and with both hoping to use their play as leverage for a new deal (either in Pittsburgh or somewhere else), at what point will more frequent flip-flopping create friction between the two, or a divide among the team? Can Smith find a balance that fosters both productivity and harmony?

The answer to that question may ultimately decide Pittsburgh’s season. For the Steelers to make a deep playoff run, they will need their offense to play well against some of the league’s better defenses. Playing both quarterbacks could be a key to doing so. Or, it may backfire. Few coordinators have been able to hit the sweet spot that allows them to move seamlessly between quarterbacks 1 and 1A. For the sake of Pittsburgh’s season, Smith needs to be the exception to this tendency and not the rule.