The loss came in the Hall of Fame Open, an official tournament of the lower-level ATP Challenger tour, which effectively made Mr. Ackman a tennis pro, if only for a day. It fulfilled a lifelong ambition — and, more than likely, he said, ended his career.

Billionaire hedge fund manager Bill Ackman competed in a professional doubles tennis match at the International Tennis Hall of Fame in Newport, R.I. on Wednesda

Pershing Square Capital Management's billionaire chief has sold most of his fund's stake in Chipotle over seven years, and is now piling into his new favorite stock.

The reprieve, while temporary, provided the perfect match to light what had become a deeply oversold stock market, launching a rally so significant that the S&P 500 has risen about 25% in the matter of only three months.