When the new school year starts in the fall, student athletes will have a harder time arguing against being sidelined after a head injury.

A new state law signed by Gov. M. Jodi Rell Wednesday requires coaches to keep athletes off the field for games and practice if they show any signs of concussion, such as confusion, blurred vision, severe headaches and balance problems. They cannot play again until a doctor gives the OK. Coaches who fail to follow the law risk losing their coaching permit.

The law, which takes effect July 1, also requires coaches to take a training class in the signs and symptoms of concussion before the start of the fall season, and a refresher course every five years.

The legislation was supported by both parties and endorsed by coaches, teacher and parent groups, physicians, the Brain Injury Association of Connecticut, the Connecticut Association of Schools and the Connecticut Interscholastic Athletic Conference.

Because their brains are still developing, teen athletes in particular are vulnerable to serious, long-term injuries from concussions, particularly if they go back out on the field or court too soon, according to supporters of the bill.

In Connecticut, about 107,000 youth play high school sports, and about 5,000 to 8,000 have concussions each year, according to the CIAC.

The Center for Injury Research and Policy, at Nationwide Children's Hospital in Columbus, Ohio, estimates there were 400,000 concussions in U.S. high school students between 2005 and 2008, most in football players. But lacrosse, soccer and basketball players, wrestlers, gymnasts and cheerleaders were also among those who suffered concussions.

The center's research also shows that 40.5 percent of those injured student athletes went back on the field or court too soon. The center's research was cited by state Sen. Thomas Gaffey, D-Meriden, who introduced the bill along with state Senate Majority Leader Martin Looney of New Haven.

j.benson@theday.com