Inside the often-chaotic NFL challenge process

"Unless it's egregious, they're going to go with the call," said former coach John Fox, who didn't like to challenge the spotting of the ball. "You ain't winning that."

Replay challenges loomed large in both conference title games Sunday, including on a play that led to a touchdown early in the Philadelphia Eagles' win over the San Francisco 49ers.

An NFL sideline is a hive of activity, bustling and buzzing for three emotionally exhausting hours every week. The next playcall, the personnel, the play clock -- each must be shrewdly and simultaneously managed, all while reacting to your opponent's countermoves.

The stories behind how these decisions are made can range from fascinating to frustrating. But the outcomes can alter the shape of a season or -- depending on the magnitude of the contest -- change the trajectory of careers.

Here's a look inside some of the most chaotic -- and most critical -- moments in an NFL game: The precious seconds preceding a coach's replay challenge.

NFL TEAMS HAVE evolved their processes for handling replay challenges over the years to the point it's now become a somewhat specialized area for staffers on many teams. For a number of clubs, game-management coaches are charged with quarterbacking their team's challenge decisions, taking advantage of the television broadcasts playing on screens in the coaches' booths and their mastery of the highly complicated replay rules.

On other teams, the job might fall to another member of the coaching staff. In either case, most teams have a clearly identified procedure for communicating information to the head coach, who ultimately decides whether to throw the red challenge flag. Niners coach Kyle Shanahan calls his point man -- vice president of football administration Brian Hampton -- "a straight computer. He's extremely smart."

But make no mistake: This is not a simple process, no matter who is assisting a coach.

Try reaching a clear-headed conclusion when your players are urgently advocating their view of the play, the crowd is roaring in an effort to influence the decision and your coaches upstairs are wavering.

That's to say nothing of the considerations related to the game situation, the number of remaining timeouts and ensuring proper interpretation of the applicable rules governing the play and the replay procedures themselves.

"It's a highly stressful situation for everybody," said ESPN officiating analyst John Parry, a former NFL referee.

In the earlier scenario, Reid made the right call. He challenged the spot of the ball and the call was overturned, giving the Chiefs a first down at the Bengals' 19-yard line.

Three plays later, Patrick Mahomes hit Valdes-Scantling for the go-ahead touchdown as the Chiefs went on to win 23-20.

"I feel for the coaching staffs," Parry said. "I have empathy and sympathy for them in [their] attempt to try to remember and retain and stay up to speed with an extremely complicated instant replay system."

Additional levels of intricacy are added each time replay rules are amended by the league. One innovation added last season was the replay assist procedure that allows the on-site replay official and the NFL's officiating department in New York to intervene in situations where there is "clear and obvious" evidence to either affirm or reverse a call made on the field.

But these decisions generally come before the play clock reaches 20 seconds. If a coach throws the challenge flag before that point, any ongoing replay assistance ends and the formal challenge procedures kick in.

"If [the play clock] gets to 20 and [lower], that's when a coach's flag should be thrown," Parry said. "Some coaches throw the flag at 26 seconds and then they're like, 'Why wasn't that a replay assist?' Well, you threw it too quick."

It isn't always clear to fans when the replay assist process is utilized since it is designed to avoid stoppages in play. But a good clue is to pay attention to times when a referee indicates a call was changed "after discussion." That discussion, Parry said, is typically with the replay assistant and league office.

Some wondered why a replay assist wasn't used Sunday when Eagles receiver DeVonta Smith was credited with a 29-yard reception that led to a touchdown on Philadelphia's first drive. Replays on Fox showed the ball hitting the ground.

But the Eagles rushed to the line of scrimmage after the play, apparently snapping it before replay officials could take a close look. The Eagles ended up rolling to a 31-7 victory, so the situation didn't factor into the game.

In Shanahan's defense, coaches are at the mercy of the television broadcasts or in-stadium replays, something that has a significant impact on the timing of these situations.

"The replay we saw didn't definitively show that [it wasn't a catch]," Shanahan said after the game. "I was going to throw one anyways, just to hope to take the chance, but they showed one up on the scoreboard that didn't have all the angles you guys saw, and that looked like a catch. So we didn't want to waste a timeout, which we definitely would have if we didn't see that.

"Then I heard they got a couple other angles, and you guys ended up seeing later that it was not a catch."

While the designated replay official in each stadium has a real-time view of every camera angle, coaches only have access to the network version of the game.

That might have been a factor in a Week 7 scenario that prompted Detroit Lions coach Dan Campbell to throw his headset in frustration. Campbell was awaiting advice from Jon Dykema, who is the Lions' director of football compliance and lead football counsel, and also the person in the booth who advises Campbell on challenge situations. There was a possible scoring play by tight end Brock Wright, who was ruled down at the 1-yard line. But when no immediate advice was forthcoming, Campbell had the offense line up and try to score on first-and-goal. That's when running back Jamaal Williams fumbled and the Dallas Cowboys recovered.

Detroit was trailing 10-6 at the time before losing 24-6. A touchdown in that situation would have markedly changed the complexion of the game, although replays seemed to indicate Wright was stopped short of the goal line.

"I was waiting to get a call and I didn't get a call," said Campbell, who later explained there was a technical malfunction. "At that point, let's go. Line up and play ball."

That example speaks to the timing element of these critical situations, with important, complex decisions being made on the fly under duress.

There's also the reality of coaches needing to honestly interpret what happened versus what they want to believe happened. Green Bay Packers coach Matt LaFleur was perhaps guilty of the latter in a Week 4 meeting with the New England Patriots. In that game, he challenged a dropped pass by Romeo Doubs against the advice of his assistant quarterbacks coach Connor Lewis, who advised LeFleur from the coaches booth to not challenge.

"I'm not too proud of that moment," said LeFleur, who lost the challenge and, thus, a timeout. "That was an emotional decision, and I think it's a great learning lesson that you can never make those emotional decisions in the heat of battle. You know better."

YOU'VE PROBABLY NEVER watched a football game and wondered how many cameras were filming the action. But Zac Taylor does it all the time.

Before each game, the Bengals coach and his team's data analyst, Sam Francis, review possible camera angles that could show various views on replay. Their diligence played at least some role in their decision to not challenge a possible Ja'Marr Chase touchdown in Week 1, a decision that was thoroughly second-guessed.

"Part of it was, that's the hardest place for us to see in the entire field," Taylor said of the visiting sideline end zone angle. "So, I didn't think there was a chance."

Here again, we see another example of the complexity coaches are dealing with as they reach these decisions.