A state lawmaker from Westport on Tuesday pitched his bill that would prohibit tackle football before eighth grade as a way to protect children from brain injuries, while opponents countered that it would infringe on parental decision-making.

"Increasingly, science is telling us that hits to the head are bad, and that the sooner they start, the younger you are when they start, they worse it is for you," Rep. Paul Schmid told the Public Health Committee.

Schmid's bill would prohibit children in grades seven and below from playing, practicing and otherwise participating in "organized tackle football," with flag football and other non-tackle varieties still allowed.

Schools, leagues or other entities that violate the prohibition would be subject to a fine of up to $2,000 per violation, with penalties increasing for subsequent violations and for "serious physical harm" to participants.

Responding to a question from committee co-chair Sen. Jo Comerford about how fines would be enforced, Schmid said that this is his first session filing the bill in an attempt to raise the issue for discussion, and that the details are still in development.

The bill (H 2007) is titled "An act for no organized head impacts to schoolchildren," or "NO HITS." Aside from Schmid, a Democrat, it is cosponsored by 16 other representatives -- six Republicans and 10 Democrats.

Dr. Robert Stern, director of clinical research for Boston University's Chronic Traumatic Encephalopathy (CTE) Center, said Massachusetts has made "tremendous gains" in protecting athletes from concussions, but a "growing body of research" shows that it's not just the "big hits" that can affect players' brains. Repetitive sub-concussive hits that can be part of routine game play can also cause short-term and long-term neurological consequences, he said.

"Football is to CTE what smoking is to lung cancer," said Chris Nowinski, a former professional wrestler and Harvard football player who co-founded the BU CTE Center and is the founding CEO of the Concussion Legacy Foundation. "The more you do it, the longer you do it, the greater your risk."

Nowinski referenced a recent study by BU researchers that found the risk of developing the degenerative brain disease CTE rises by 30 percent with each year of playing tackle football.

Paul Dauderis of the Massachusetts Youth Football Alliance urged the committee members to seek out research that specifically focuses on youth and high school football players, saying many studies examine the small number of athletes who play at the college and professional levels. He called Schmid's bill a "tremendous overreach into the rights of parents to allow their children to play a game."

Jon Butler, executive director of the Pennsylvania-based youth football organization Pop Warner Little Scholars, said youth football is safer today than it's ever been in the past, thanks to changes including mandating coach education, new "medically guided" rules, and a greater awareness of concussions. He said there has not yet been a study that shows the effect of delaying the age at which a child starts tackle football.

"Once tackling is introduced, athletes who have no previous experience with tackling would be exposed to collisions for the first time at an age at which speeds are faster, collision forces are greater and injury risk is higher," Butler said. "Lack of experience with tackling and being tackled may lead to a substantial increase in the number and severity of injuries once tackling is introduced, and that is a very important point that we are concerned about."