BOSTON — One of the nation's first professional baseball players lies largely forgotten by history in an unmarked grave in Boston.

Now, nearly 150 years after Andrew Jackson Leonard began his professional career, his grandson hopes to raise enough money for a marker to honor his relative and his contributions to the game by auctioning his grandfather's contracts, which are among the oldest known in existence.

“He was one of the original boys of summer and we need to do what we can to promote his legacy,” said Leonard's grandson, 82-year-old Charles McCarty.

Leonard was born in County Cavan, Ireland, in 1846 and moved to the United States with his mother and siblings when he was 2 years old to escape the potato famine, McCarty said.

The family settled in Newark, New Jersey, where Leonard started turning heads as a baseball player.

He played for the Cincinnati Red Stockings in 1869, baseball's first professional team. But it's an 1871 contract Leonard signed to play for the Washington Olympics that is perhaps the most historically significant artifact, said Chris Ivy, director of sports at Dallas-based Heritage Auctions, which is handling the sale.

It was signed at a time when there was a societal rift over whether baseball should pay its top players or remain amateur. Written on U.S. Treasury Department letterhead and signed by the acting Treasury secretary, the 40-word contract promises Leonard $720 for one year to be a department messenger.

“That contract sheds light on what's long been believed but not proven, which was that there were professional baseball players posing as amateurs who were getting paid under the table for no-show jobs, and this is tangible evidence that the government was involved,” Ivy said.