Aggressive fourth-down play-calling could not give Brock Purdy a functioning throwing elbow. By the fourth quarter of the January 2023 NFC Championship Game, San Francisco had also lost Josh Johnson to a concussion. Kyle Shanahan still had a game to chase, but essentially no quarterback left who could threaten Philadelphia through the air.
The Eagles knew it. Trailing 28–7, San Francisco faced fourth-and-two near midfield and handed the ball to Deebo Samuel. Fletcher Cox and Avonte Maddox swallowed the run for a four-yard loss, according to the Eagles’ official game recap. Two yards might as well have been twenty.
Shanahan had kept his offense on the field. What he could not keep was the uncertainty that usually made it dangerous: the possibility of a throw behind an attacking linebacker.
That distinction gets lost when an injured team starts punting. Sometimes the coach has become too cautious. Elsewhere, the same fourth-and-short now asks different players to execute a play they cannot reproduce. The question starts with who can still block, throw, and get open.
Reid put the season in Henne’s hands
Two years earlier, Andy Reid faced his own playoff reckoning with a backup quarterback. Patrick Mahomes had left Kansas City’s divisional-round game against Cleveland after entering concussion protocol. Chad Henne inherited the offense, and the Browns kept coming.
With the Chiefs protecting a five-point lead, Henne scrambled for 13 yards on third-and-14. He finished just short. Reid now faced fourth-and-one from his own 48, with 1:14 remaining, according to the official game book.
A punt would give Cleveland another chance to end Kansas City’s season. Reid called a pass.
Henne took the shotgun snap and threw right to Tyreek Hill. Five yards later, the Chiefs could kneel out the game. Kansas City’s official recap records the completion that secured the 22–17 victory.
The tension came from everything that could have gone wrong. Henne had already thrown an interception, and a failed fourth-down attempt would have handed Cleveland the ball near midfield. Reid trusted the specific throw anyway.
That helps explain why some injuries leave a coach room to attack while others strip away his best options. Kansas City still had a quarterback capable of delivering the ball and Hill available to catch it. San Francisco had reached a far more desperate condition.
Neither game proves that injuries consistently make NFL coaches more conservative. Together, they show why the backup’s actual capabilities matter more than his place on the depth chart.
The yard stays the same. The odds don’t.
The yard marker offers a clean number. Football supplies the complications.
When the NFL introduced its Next Gen Stats Decision Guide in September 2021, it published estimated conversion probabilities of 77% for fourth-and-inches and 72% for fourth-and-one. The point was precision: two plays carrying similar descriptions could leave an offense meaningfully different distances to travel.
Personnel adds another complication. The NFL’s explanation explicitly recognized quarterback quality as relevant to conversion chances. A short throw with Mahomes available does not present the same problem as that throw after he leaves.
Those historical percentages do not demonstrate that NGS automatically recalculates every injury’s effect in real time. The published explanation does not establish that capability. Their relevance here is narrower: even the exact ball placement changes the estimate, so a generic fourth-and-one percentage cannot settle a personnel-specific decision.
Going for it requires two judgments. How likely are these players to convert? What does converting—or failing—do to their chances of winning?
Researchers Ryan Brill, Ronald Yurko, and Abraham Wyner explored uncertainty in those decisions in “Analytics, Have Some Humility,” revised in January 2025. They found that estimates of the best fourth-down choice carried more uncertainty than popular sports analysis generally conveyed.
Consider a hypothetical recommendation favoring an attempt by one percentage point of win probability. That small edge deserves scrutiny if the offense has just lost the player its preferred call depends on. It does not automatically justify a punt, either: the coach still has to weigh the cost of giving possession away.
Help the tackle, lose a receiver
Start with a hypothetical absence of Trent Williams. On a left-side run, the question becomes brutally specific: can his replacement move the assigned defender, or reach him before he closes the lane?
If the answer requires help from a tight end, the offense must account for that extra blocker. On a passing play, keeping the tight end beside the tackle can remove a receiver from the pattern. The quarterback gains protection but loses somewhere to throw.
That tradeoff can make fourth down harder with a healthy starter under center. A coach may still call the same formation while knowing he cannot release every eligible receiver.
The running back matters, too. Against pressure, a replacement must recognize which defender belongs to him and meet that rusher before the pocket breaks. His rushing average cannot answer that question.
No St. Brown, no easy substitute
Consider a hypothetical fourth-down package designed around Amon-Ra St. Brown getting open inside. If he leaves, Detroit cannot assume another receiver will reproduce the same release, timing, and understanding with the quarterback.
The replacement might need a different route or help from motion. That adjustment can change the quarterback’s read and the protection’s required duration.
A short-yardage gamble can turn on any of those details. Removing one starter can force several teammates to do something different, all within a snap that offers no second attempt.
Give the backup a winning play
The preparation starts before a trainer waves toward the sideline. A backup quarterback needs practice snaps on the short-yardage throws the coach would actually call with a game hanging over them.
Those repetitions should include the surrounding replacements. A throw means little if the reserve tackle cannot sustain its protection. Timing also suffers when a receiver and quarterback disagree about where the route should break.
Coaches should build a small set of dependable answers around those players. One replacement might handle a quick rollout comfortably. Another might offer more on a sneak or a handoff with a simple pass option attached.
The same work should establish what the offense must abandon. Keeping a favorite play on the call sheet serves nobody if its essential block now requires help the formation cannot provide.
The confidence to keep the offense on the field should emerge from that preparation. A coach needs a reason to believe this group can gain this yard against this defense.
He also needs to remember what a punt costs. An injured defense may struggle to return the ball, making a difficult conversion attempt the better remaining chance.
Reid could still ask Henne to find Hill. Shanahan could no longer make Philadelphia respect a downfield throw. When the next starter limps off, the decisive question will arrive before the punt team moves: which dependable answer remains on the call sheet?
READ MORE: Why punt hang time is a critical metric for NFL special teams rankings
FAQs
Why do injuries change fourth-down decisions?
Injuries can remove the blocks, throws, or receiving matchups a play needs. Coaches must judge whether the replacements can still gain the necessary yards.
Should NFL teams always punt when the starting quarterback gets hurt?
No. Chad Henne’s completion to Tyreek Hill shows that a backup can execute a decisive fourth-down play when the right matchup remains available.
What happened to the 49ers’ quarterbacks in the 2023 NFC Championship Game?
Brock Purdy injured his throwing elbow, and Josh Johnson left with a concussion. San Francisco had almost no passing threat left.
Does Next Gen Stats automatically adjust for every injury?
The published explanation discussed in the article does not establish that. Its historical conversion percentages cannot settle every decision involving replacement players.
How can an offensive tackle injury affect fourth-down passing?
A tight end may need to stay in and help the replacement tackle. That gives the quarterback extra protection but one fewer receiving option.
