Last fall, the National Football League scored a huge victory in California, helping push through a new law barring most professional athletes from filing workers’ compensation claims in the state. The NFL, successfully lobbied the state legislature to pass AB 1309, which prohibits athletes who spent most of their careers playing for teams outside California from filing claims in the state. The leagues believed the law could save them from exposure to countless claims from injured athletes. But that win has come at a cost.

The Los Angeles Times reports that publicity from a high-profile battle over the legislation prompted players from around the country to file more than 1,000 injury claims just prior to a September deadline – a huge influx that could cost the nation’s top professional sports leagues hundreds of millions of dollars to resolve. In the first two weeks of September, current and retired players filed 569 claims against NFL franchises, 283 claims against Major League Baseball clubs, 113 against National Hockey League teams and 79 against NBA squads. Nearly 70% of the filings include allegations of head or brain injuries caused by repetitive trauma. Most of these athletes appeared to have never played for a California team; they filed claims based on repetitive injuries they say were sustained in part during road games played in the state. It is those claims that are now barred under the new California law.

Among the athletes rushing to beat the deadline were sports legends such as Miami Dolphins quarterback Dan Marino, Baltimore Orioles pitcher Jim Palmer and Houston Rockets center Hakeem Olajuwon, as well as many lesser-known retirees, some suffering serious physical impairment. A number of active players, including San Francisco 49ers standouts Michael Crabtree and Frank Gore, also filed claims.

The six sports leagues affected by the new law – a group that includes Major League Soccer and the Women’s NBA – had predicted a jump in filings before the deadline. Still, the size of the increase was surprising. The volume of claims in September was about 10 times higher than average monthly levels since 2011. The workers’ compensation data highlights the huge scale of the injury legacy that confronts American professional sports franchises. More than a third of the final batch of claims lodged before the new statute became effective Sept. 15 wouldn’t have been affected by the new law, the Times analysis found. Advocates for injured athletes say that the months-long fight over the bill, which drew national attention, helped alert athletes who otherwise wouldn’t have known they could seek benefits.

More than three-quarters of the claims filed against NFL teams in the first two weeks of September alleged head or brain injury. Half of baseball players and just over 90% of hockey players made similar claims. An NFL study of past filings found that the average California claim cost teams $215,000 to resolve, a number that could be far higher for players with debilitating brain disease. Unlike other states, California long permitted claims from players who did not play for in-state teams so long as they participated in at least one game or practice here. California also recognizes cumulative injuries incurred over time. And although California has a one-year statute of limitations for claims, that restriction is waived when workers aren’t properly notified of their right to file, which was the case with many players for decades. As a result, many athletes with slow-to-develop disease such as dementia turned to California when legal doors in other states had long been shut.

In anticipation of that deadline, workers’ compensation attorneys scrambled to find players and file on their behalf. San Diego lawyer Ron Mix squeezed in almost 300 athlete cases in the final month, according to state data. To get through the mountain of paperwork, he said he paid his staff triple overtime and hired numerous temp workers. “We were working 12 to 16 hours a day, seven days a week,” said Mix, a former Hall of Fame lineman for the San Diego Chargers.

The Times analysis showed that 363 of the 1,064 claims made in the first two weeks of September listed a California-based team as the employer, indicating they likely didn’t need to beat the Sept. 15 deadline. In addition, a number of still-active players filed injury claims, something that rarely occurred in the past because players feared being cut by their teams.

“Everyone wanted to beat the deadline,” said Mel Owens, a Laguna Hills attorney and former Los Angeles Ram linebacker. He filed more than 250 claims for athletes in the final push, according to the analysis.

Overall, between February, when the bill was introduced, and Sept. 15, a total of 1,980 athlete claims were filed in California – compared to 1,170 in all of 2012. More claims were filed in that nine-month period than any other year, by far, the analysis found. Although it’s impossible to determine how many athletes will be barred from filing under AB 1309, attorney Mix estimates it could top 4,000. In recent months, he said he’s gotten calls from about 150 athletes that he had to turn away because they missed the deadline.