NEW YORK – Sean George knelt in the Church of St. Paul the Apostle in Manhattan. He wasn’t praying. A gash below his right brow bled into his eye and down his nose before a knee to his groin sent him to the floor.

George, 39, head of credit-derivatives trading at Jefferies Group, was making his Muay Thai debut at the church June 22 in a sport that allows kicking, elbowing and kneeing. His eye was swelling shut by the time he lost in a split decision.

It was the happiest he has been all year, he said.

“Right now at work I’m making less risk decisions – and I enjoy taking risks,” said George, who headed investment-grade credit-default-swap trading at Deutsche Bank before he joined Jefferies last year. “If you’re in it for the game and the fight, the game’s over and the fight’s over.”

Wall Street set pay and profit records half a decade ago by wagering billions of borrowed dollars on lightly regulated products that didn’t exist a generation earlier. Now, the excitement and rewards that swelled even after the financial system almost collapsed in 2008 have been replaced by restrictions and malaise, according to interviews with more than two dozen current and former bankers and traders.

Some, like George, are seeking their kicks in less regulated jobs.

Others say they’re struggling to cope as JPMorgan Chase & Co. is being investigated for trades that caused at least $5.8 billion in losses, Goldman Sachs reported the worst first half since before Lloyd Blankfein became chief executive officer in 2006 and Barclays was fined a record $450 million for trying to rig global interest rates.

Banks face new restrictions designed to prevent another global credit crisis. Limits on proprietary trading, or bets with firms’ own money, and rules requiring them to hold more capital make it more difficult to use borrowed funds to boost returns. As the European sovereign-debt crisis escalates and economic growth in the United States and China slows, clients are refraining from the deals that power Wall Street profit.

“There’s no sexiness, there’s no fun; there’s no intellectual intrigue, either,” said Ethan Garber, who ran proprietary credit-arbitrage portfolios for Credit Suisse and Bear Stearns Cos.

Wall Street’s five largest banks – JPMorgan, Bank of America, Citigroup, Goldman Sachs and Morgan Stanley – reported the lowest first-half revenue since 2008, and their leverage has dropped an average of 44 percent. Shares of the firms are down an average 33 percent in the past 12 months, four times as big a decline as the 81-company Standard & Poor’s 500 Financials Index.

Bonuses fell by 20 percent to more than 40 percent at the major commercial and investment banks last year, compensation-consulting firm Johnson Associates reported.

Robert McTamaney, who helped run Goldman Sachs’s equities-trading business in Asia until last year, likened the shift on Wall Street to a “dulling down of the colors.”

“The socks are higher, the skirts are longer,” he said. “It’s like styles: They change, and you’ve got to change with it or be left behind.”

Another former Goldman Sachs partner, Robert Jones, mourned the loss of the joys of experimentation in banking.

“The increasingly detailed and micromanaged regulatory environment has taken a lot of the fun out of the game.”