Fewer young Packers are signing up for Pop Warner football. (Mike Roemer/AP)

In 2010, just under 249,000 kids in the U.S. played Pop Warner football. That number was a record for the organization. In a new report for ESPN's "Outside the Lines," Mark Fainaru-Wada and his brother Steve Fainaru reveal that after years of steady growth, Pop Warner participation dropped more than 9 percent over the next two seasons. Mark Fainaru-Wada joined Bill to talk about the numbers.

BL: That decline happened as concerns about concussions have become one of the top stories in football. Is there evidence to show that that is the primary factor behind the decline?

MF: Well, Bill, there was no survey data done about why players dropped out or why their parents pulled them out. You know there are two people associated with Pop Warner who are intimately involved in this issue, particularly the concussion issue, including the medical director of Pop Warner, Julian Bailes, a former Pittsburgh Steelers neurosurgeon who says flat out he thinks this has to be the number one cause. And it seems that it would be naive to believe that wasn't a major role in this decline.

BL: Have you any sense of what else might have contributed to the dip?

MF: It was suggested by others that increase specialization by young people — so if they're a baseball player and a football player that they're encouraged to specialize in a sport. But that's been going on for a while, frankly. The down economy was cited also. Are there other leagues out there that players are moving to, flag football for example. There's again a number of theories and no one has really asked the question of why do people move.

BL: In 2012, Pop Warner football altered some of its rules about practice to try to limit head injuries. Tell us a little bit about what they've done.

MF: One thing they did was limit the amount of hitting time during practice. As well, they've eliminated what often became a popular but destructive way to hit where you would have players lining up like three yards apart or less than that and really just going at each other. They're looking at even more dramatic suggestions. One idea that Julian Bailes, the medical director, has forwarded is the idea of taking players out of the three-point stance and having them standing up.

BL: How much supervision is there as far as individual coaches in Pop Warner football? Because it seems to me there still could be guys who hold out for the old ways.

MF: You know there's a new program that the NFL is largely behind with USA Football, which is the governing body for the sport, called Heads Up. You have to go through a process to be in Pop Warner, but at the same time as we talk to people just anecdotally, you hear there's different people coaching in different ways. So, I think there's an effort to become more uniform around the way they teach tackling and hope that that can help mitigate against some of the injuries we've talked about.

BL: Dr. Robert Cantu is with Boston University's Center for the Study of Traumatic Encephalopathy and he's an adviser to the NFL. He has said that kids under the age of 14 shouldn't play tackle football. Pop Warner players start as young as five, so that would be devastating to their program. Does Dr. Cantu's position have any momentum?

MF: You know, I think it remains to be seen. I think there's no question if you look at some of the surveys that have been done recently around concerns by parents about the sport, HBO and Marist just did a survey about this, I just read a Robert Morris survey about this, there's huge concerns obviously among parents about this. And I think that's reflected obviously in the data here. Again it's all anecdotal at this point, but it's been suggested that there are increases in the flag football leagues and that you might see players moving towards flag football a little more prior to tackle. The argument against that though is the coaches will tell you, look if players are going to play tackle football, they're going to need to learn how to hit. Some have suggested that waiting till high school is too late. I think again we have to wait and see and also we have to wait and see where the research takes us on that.