A wild scramble commenced on the afternoon of March 28. NFL owners had approved a fundamental overhaul of kickoffs, agreeing to implement a structure so different from tradition that competition committee chairman Rich McKay ranked it among the league's most substantial rules changes of the past 30 years.

The timing left teams 163 days before the regular season starts to practice the new alignment, which the NFL projects will more than double the rate of returns from the 2023 season and add about 1,000 plays to games over the course of the season.

The list of questions seemed endless:

• Given the basic premise of the redesign -- less downfield running and more incentives to return -- what personnel changes would be needed?

• How many returners should be on the field?

• What is the ideal kick trajectory and placement?

• Are there ways to shield kickers from risking injury amid the potential projected uptick in being involved in tackles?

• How would field position be affected?

• What other peripheral side effects should be expected?

• Most notably: Will it produce as many returns as the NFL hopes?

ESPN spoke with coaches, players and analytics experts this spring as they rushed to prepare. Many echoed the uncertainty of New Orleans Saints coach Dennis Allen, who said: "There's nobody that knows what this kickoff is going to look like. That's the reality. It's never been done [in the NFL] before."

Teams didn't throw their hands up. Instead, they devoted more attention to special teams during OTAs and minicamps than ever, experimenting and musing publicly on ideas as eccentric as using position players as kickers to minimize injuries or a 12th man to hold on windy days.

They've reported to training camp this month with plans to refine their approaches and test them in preseason games, and they'll do it in the context of NFL gamesmanship -- measuring the necessity of seeing their ideas in live action against the instinct to cloak strategies until the regular season.

"This is the coolest thing to happen in terms of my coaching career," San Francisco 49ers special teams coordinator Brian Schneider, a veteran of 14 NFL seasons and another 16 on the college level, said. "It's, 'What are you going to do?' You have a great opportunity to do something that's never been done before. So it's a race to figure it out and it's going to be constantly adjusting."

New England Patriots kicker Chad Ryland said: "It's almost like a horse race, like a Kentucky Derby. Who is going to get out of the gate fast and keep that lead with new discoveries?"

What are the kickoff rules changes?

For nearly two decades, the NFL tried to lower the high concussion rate on kickoffs -- three to five times the typical rate of offensive plays the past decade -- by introducing rules to reduce returns. Its newest rules changes, however, are modeled after what the XFL implemented in 2020 and used again in 2023 -- an effort focused on reducing high-speed collisions rather than returns. But there are enough differences between the two versions that NFL coaches consider the XFL structure more of a rough guide than a blueprint.

The thinking for both leagues is based on two theories. The first is that high-speed collisions that cause concussions can be reduced by lining up most players downfield before the kick rather than having them run after it. The second is there are ways to incentivize returns and discourage touchbacks.

The NFL softened some of the XFL's ideas, compromises to gain owners' approval. In the NFL, 10 members of the kickoff team and nine or 10 members of the return team will line up on the returning team's 40- and 35-yard lines, respectively. In the XFL, they were at the 35- and 30-yard lines, putting them closer to the returner and giving them less ground to cover.

The NFL's hybrid kickoff for 2024. pic.twitter.com/enyoNNEnSp

Kevin Seifert (@SeifertESPN) March 26, 2024

The NFL rule allows up to two returners, creating changes in potential blocking schemes. And the XFL used more extreme rules to discourage teams from kicking the ball out of the end zone, most notably spotting touchbacks at the 40 instead of the 30 in the NFL. The XFL also lined up its kickers at their own 30, rather than the 35 in the NFL, and required everyone but the kicker and returner to stand still for three seconds if the ball hit the ground.

For those reasons, plus the presumed superiority of its kickers, the NFL has projected its kickoff return rate will rise from 21% in 2023 to about 55% in 2024. (The XFL return rate in its 2020 and 2023 seasons was 93%.)

"But we've been pretty clear that this is something that is hard to estimate," NFL senior director of football data and analytics Michael Lopez, who leads the group that made the projection, said. "This is not a play that we can know for sure. We are guessing, using what the special teams coaches are telling us and what the data from the XFL told us, and then sort of guessing and imputing where the teams will kick off to."

Two returners? Kickers making tackles?

Where teams kick off to was perhaps the most intense focus of spring practices -- more than identifying returners and determining what types of players were best-suited for coverage and blocking assignments. While it's safe to say there will be more returns in 2024, teams have in no way conceded they will be productive returns.

Many coaches are leaning into an under-discussed aspect of the new rules: A touchback will be spotted at the 20-yard line if the ball lands in a "target zone" (between the goal line and the 20), bounces into the end zone and is downed. From the kicking team's perspective, Denver Broncos coach Sean Payton said, "the perfect kick goes inside of the [target zone] and into the end zone."

As a result, most teams are likely to deploy two returners to ensure they can pick up those bouncing balls before that happens. And that provides the kicking team with its best chance at winning the play: tackling a returner who picks up a bouncing ball before he gets to the 20.

"We're trying to get the ball on the ground away from the returners as quick as possible," Kansas City Chiefs special teams coordinator Dave Toub said.

XFL teams didn't attempt many return-killing kickoffs, largely because of the talent level of their kickers. But, Lopez said, "We're more confident that NFL kickers will be able to kick it to the back of the landing zone, and we'll have a lot of returns with the return team starting somewhere around the 2- or 3-yard line."

Some teams have wondered whether putting the ball in play so often will expose kickers to injury if they have to make a tackle. The Chiefs, for instance, spent part of this spring considering whether to remove kicker Harrison Butker from kickoffs and use safety Justin Reid -- who attempted two extra points and kicked off seven times in emergency duty during the 2022 season -- instead. Baltimore Ravens kicker Justin Tucker, meanwhile, said he put on a few pounds this offseason to prepare for contact.

It might all be for naught. The NFL rule prevents kickers from crossing the 50-yard line until the ball is caught or hits the ground, reducing the chances that they'll get close enough to be involved in tackling. Plus, Los Angeles Rams special teams coordinator Chase Blackburn said most teams won't have a position player who can match Reid's dual skills.

The consequences of kicking mistakes are severe: If the ball hits the ground before the 20-yard line, or if it goes out of bounds, it will be spotted at the 40.

"You don't want to start too many drives like that," Blackburn said. "And I'd say there's not too many position players that you could bank on having 80% of the kicks without a traditional [kicking background]."

RBs instead of WRs, plus a twist?

Most special teams coaches agreed the kickoff will shift from being speed based to power based.

"It's more like offense-defense," Blackburn said. As a result, many teams are considering the merits of stocking their return teams with bigger players who are comfortable blocking what would amount to modified run schemes.

Kickoff units will need to make sure their cover men are big enough to take on those blocks, and returners are more likely to be "a running-back-style type guy," Toub said, because the one who doesn't field the ball will need to block.

"So they have to be not only a good returner," Toub added, "[but also] be able to take a hit and bounce back from a lot of tackles."

Teams will work through schemes during training camp, often in public view. What they are almost certain to shield from observation, however, is how the new set of rules will impact their game management strategies. Saints special teams coach Darren Rizzi, however, gave reporters a glimpse.

For instance, the last-minute compromise to spot the touchback at the 30-yard line, from the 35 as originally proposed, will make an intentional touchback palatable in certain situations.

"[If] now all of a sudden we have a two-score lead," Rizzi said, "and I don't want to run the risk of [opponents] getting great field position, that's where I think you're going to see teams say, 'Screw it, we'll give the 30 and we don't want to run the risk of them returning it to midfield.'"

There is another twist to consider. For years, smart returners tried to capitalize on the rule that spotted the ball at the 40-yard line if a kickoff went out of bounds; the returner would try to field the ball with a foot already out of bounds. This season, there will be an additional way to pursue this strategy: touching the ball beyond the 20-yard line, triggering a new rule that spots the ball at the 40 if the kick hits the ground or is fielded there.

"If I'm a player ... and I get myself up over the 20-yard line and touch the ball, I'm [essentially] out of bounds," Rizzi said. "That's something we've never, ever seen before, because the 20-yard line will be officiated just like the out-of-bounds line. So essentially you now have a third out of bounds line added to the field on kickoffs. ... And so that's going to be a really interesting aspect of it."

Most players interviewed by ESPN, especially returners, struck cautionary tones in the midst of spring practices. Saints running back Alvin Kamara, who was a primary returner earlier in his career and could resume that role in 2024, said: "If I've got to do it, I'll do it. It is what it is. Not that I don't like [the changes], but it's just something else to adapt to."

Side effects of the new rules

Teams are bracing for an impact far beyond the actual return numbers. Three other metrics could change in significant ways: the variance of field position, fourth-down attempts and punt totals.

Last season, for instance, 88% of kickoffs resulted in teams taking possession between the 21- and 30-yard lines, largely because touchbacks were spotted at the 25-yard line. Lopez and his team project that percentage will drop to between 40% and 50% in 2024. If that's the case, Lopez estimates around 14% of possessions will start inside the 20 and about 41% past the 30.

"There's uncertainty there," he said. "But the main thing is that you're getting a larger bucket of plays that'll start past the 30 and you're getting a larger bucket of plays that'll sort of start inside your 20. And those are all exciting plays. That's a big stop for the kickoff team or it's a big return for the return team."

As a result, the NFL is anticipating offenses will try more fourth-down attempts and fewer punts, because more possessions will start at or beyond the 30-yard line.

"[Previously,] if you had a drive starting at your own 20 or 25," Lopez said, "your fourth-and-1 is from your 29 or your 34-yard line. [With the new rules,] if you start at the 30, your fourth-and-1 is from the 39. That makes a big difference in your fourth-down model that clubs might be using."

The NFL and its teams have only a vague -- albeit hopeful -- idea of what this version of the kickoff will look like. Many believe it will evolve throughout the season, with a much different set of approaches in Week 18 than in Week 1. But every game counts, and the preseason will offer the best initial evidence of what is to come -- and who is to come out ahead.

"We're not only going to have eyes on our preseason games," Rizzi said, "[but] we're going to have eyes across the league on the other 31 teams on how people are doing things. Because I think the quicker everyone figures this out, both coaches and players, it's going to be a major advantage to certain teams."

ESPN NFL Nation reporters Sarah Barshop, Courtney Cronin, Rob Demovsky, Daniel Oyefusi, Mike Reiss, Adam Teicher, Katherine Terrell and Josh Weinfuss contributed to this story.