A federal jury in Dallas ruled on Wednesday that Mark Cuban did not commit insider trading when he dumped his stake in an Internet company clearing the billionaire entrepreneur of wrongdoing and dealing a blow to the federal agency that Mr. Cuban battled tooth and nail for five years.

The agency the Securities and Exchange Commission was hoping to build on the momentum it gained from the recent trial win against Fabrice Tourre a former Goldman Sachs trader at the center of a toxic mortgage deal.

But the loss in the Cuban case could reignite concerns about the agency’s struggles in the courtroom where some crucial cases stemming from the financial crisis crumbled. The loss on Wednesday might also undercut the S.E.C.’s campaign to hold more individuals accountable at trial a policy championed by its new chairwoman Mary Jo White.

The S.E.C. however played down the significance of the verdict.

“We respect the jury’s decision” John Nester the agency’s spokesman said in a statement. “While the verdict in this particular case is not the one we sought it will not deter us from bringing and trying cases where we believe defendants have violated the federal securities laws. ”

After just four hours of deliberation a nine-person jury concluded that Mr. Cuban was not liable under federal securities laws capping a more than two-week civil trial for one of the few celebrities to land on the S.E.C.’s radar. The 55-year-old reality TV personality best known as the owner of the Dallas Mavericks basketball team was facing a roughly $2 million fine.