Some say he's a nuisance to the NBA, with more than $1 million in fines held up as evidence. Some Mavs fans say his constant baiting of officials merely leads to more calls against the team. Even his dancing skills have been panned, drawing an early round ousting from "Dancing With The Stars."

But now Cuban is facing a much more serious allegation: The government saying he's an inside trader.

Federal regulators filed a civil lawsuit Monday accusing Cuban of using confidential information to bail out of an investment and avoid about $750,000 in losses. Cuban denies doing anything wrong and insists his name will be cleared.

Even if he loses in court, Cuban's penalties would be strictly financial — perhaps close to $3 million. Martha Stewart settled the civil part of her insider-trading case, but ended up going to prison for criminal charges related to it. Cuban isn't facing criminal charges.

"It is a fascinating case," said Harold Degenhardt, who spent nine years prosecuting securities fraud as head of the Fort Worth office of the Securities & Exchange Commission and another 25 defending them in private practice. "This is a very difficult case for the SEC. I don't think they brought it lightly."

According to the SEC case, Cuban told his broker to sell all his shares of Mamma.com after the company's CEO confidentially told him of a stock offering that would dilute the value of all existing shares, including Cuban's. By selling before the information became public and the price fell, Cuban avoided losses exceeding $750,000, the SEC said in its lawsuit.

However, on Cuban's blog Tuesday was a statement from his attorneys that cites an interview with the CEO in which he says there was no agreement to keep information confidential.

Thus, Degenhardt said late Tuesday, this could turn into a he-said, she-said trial, and those are always risky.