FOXBOROUGH - The first game of the NFL season is kind of like a piñata. You know there is going to be some type of candy inside the papier-maché punching bag, but you don't know exactly what kind until it spills out on to the floor.
In an NFL season opener, you know football players are going to play, but you don't know how they're going to perform and what it's going to look like until the action unfolds on the field.
While all NFL openers are mysterious, today's Patriots-Chiefs game at Gillette Stadium has an added element of intrigue: inexperience. Both the Patriots and Chiefs are going to have rookies making their NFL debuts in key positions.
The Patriots, who could have as many as six rookies active, are expected to start first-round pick Jerod Mayo at inside linebacker and second-rounder Terrence Wheatley at left cornerback in their 3-4 defense.
Callow Kansas City has 15 rookies on its 53-man roster, and coach Herm Edwards said 11 of them could be active today, including likely starters Glenn Dorsey (right defensive tackle), Branden Albert (left tackle), and Brandon Flowers (cornerback).
That should make an already unpredictable game even more difficult to gauge.
"They have so much to learn, experience, and absorb on every level, whether it is preparation, playing on the field, off the field, plays, schemes, techniques, situations, rules - you name it," said Patriots coach Bill Belichick. "There are thousands of things that are different between college and pro football. It is a process for them to make that transition. We try to help them as much as we can, but it is a process.
"They are not going to get it all in one day, one week, or one regular-season game. You just hope that they get as much as you give them, so they don't make mistakes based on inexperience. If they make a mistake because they get beat on the play, well, that happens to everybody. You hate to give up a play on inexperience, so you try to eliminate those if you can."
Draft picks Mayo, Wheatley, outside linebacker Shawn Crable, quarterback Kevin O'Connell, cornerback Jonathan Wilhite, safety/wide receiver/special teamer Matthew Slater, linebacker Bo Ruud, and undrafted free agent linebacker Gary Guyton have given an aging team a needed infusion of youthful energy and athleticism. All but Ruud, who is out for the year with an ankle injury, are on the team, with rookie linebacker Vince Redd, running back BenJarvus Green-Ellis, and safety Mark Dillard on the eight-man practice squad.
However, the tradeoff is that the rookies are raw. You don't know how Flowers is going to react to having to cover Randy Moss or how Mayo will respond to having to recognize a screen pass to Larry Johnson in a key spot in the game.
That is the dilemma coaches face when they plug NFL neophytes into their plans.
"[Rookies] don't know what they don't know, which is kind of good as a coach because you can kind of mold them the way you want," said Edwards. "But that being said, there are some misfires. Sometimes you scratch your head after practice and ask yourself, 'Why did he do that?' That's just part of the learning process for young players."
Even rookies who are physically prepared for the NFL can get hung up by the mental side of the game.
"The speed you have to think and the amount of checks that you're supposed to know, it's a lot different than in college where there are just a few," said Wheatley last week, before the institution of the Patriots' rookie gag order.
"Up here, there's a check on almost every play. You have to think a lot faster up here. Until you get completely comfortable, you're always going to second-guess your first reaction, because you've never seen it before, so that's going to take some time to get used to."
Even some who went on to become great players were rough around the edges as rookies. Patriots outside linebacker Mike Vrabel recalled his NFL baptism with the Pittsburgh Steelers in 1997. He played against the Dallas Cowboys - and not very well.
"I remember Nate Newton and Erik Williams slamming me to the ground because I was a rookie from Ohio State," said Vrabel. "I think the fullback, [Daryl] Johnston, crack-blocked me on one play, so I really didn't know what was going on out there. I spent more time on the turf than I did standing up."
If that happens to Mayo or Wheatley today, then the Patriots will be in big trouble.
On-the-job training is less than ideal in the NFL, which is why the Patriots have tended to lean toward veterans such as cornerback Deltha O'Neal instead of players such as Mayo, Crable, Wheatley, and Wilhite.
But today, Wheatley, whom one NFL personnel man said the Patriots are very high on, and Wilhite, who figures to see time as a slot corner in multiple-defensive back sets, will make up two-fifths of the team's cornerback corps. Crable could see time at linebacker. Slater could be back on kickoff returns.
Belichick pointed out that while the unknown is a disadvantage for rookies, it also can be an advantage. Teams don't have a lot of tape on them, and other players have never faced them. That's one problem for the Patriots and Albert, who didn't even play during the exhibition season.
"There are a lot of unknowns. That is the way it is on opening day anyway," said Belichick. "But I think more so with the number of young players [the Chiefs] have and being able to attack them."
The simple truth is that the rookies on both sides might be unreliable, but they're going to be relied on today. Other players can't try to cover for them. They just have to trust them.
"We have to. Whoever is on this team has to know their role and go out there and play and perform," said safety Rodney Harrison. "That's what we're getting paid for.
"That's our job. No matter who's here, and who's not here, we have to put that aside and move forward, and we have to go out there and execute."
Michael Vega of the Globe staff contributed to this report