SAN FRANCISCO (AP) — No. 756 is going to auction.

Barry Bonds’ record-breaking home run ball will be sold online, and fortunate fan Matt Murphy figures to be a half-million dollars richer.

The 21-year-old New York man said Tuesday he had no choice but to sell the ball — several people told him he would be taxed on the valuable souvenir if he holds onto it.

“It wasn’t hard. It was simple math. I’m upset by the decision I had to make,” Murphy said. “I wanted to keep it. I’m young. I don’t have the bank account. … It would have cost me a lot more to keep it.”

Bonds broke Hank Aaron’s record of 755 with a shot into the right-field seats on Aug. 7 against the Washington Nationals.

Sotheby’s/SCP Auctions will handle the sale at http://www.scpauctions.com beginning Aug. 28 and going through Sept. 15. The starting bid has not been determined, and auction officials estimated the ball would bring at least $500,000.

“This is the most historic baseball ever to be sold,” said David Kohler, president of SCP Auctions.

The ball from Bonds’ 755th home run hit Aug. 4 in San Diego also will be for sale on the site. The same company sold the balls from Bonds’ 700th homer and No. 715 that passed Babe Ruth for second place last season.

Everyone involved hopes the buyer is willing to at least share the ball for a period of time — if not donate it altogether — with the Hall of Fame in Cooperstown, N.Y.