[Photo:  SecondPrint Productions / Flickr]

David “Big Papi” Ortiz is becoming a player in the private-equity game.

In his first major announcement about his retirement plans since wrapping up a triumphant final season with the Boston Red Sox, Mr. Ortiz said he and a star-studded group of former players are launching Dugout Ventures, a private-equity fund that will focus on companies manufacturing the next generation of baseball equipment.

Other investors in the fund include Hall of Famers Nolan Ryan and Barry Larkin, as well as retired players Vernon Wells and Torii Hunter. Like Mr. Ortiz, the other former players say they want to be a part of Dugout in part to help reverse baseball’s declining participation rates and popularity, especially among children.

Mark Walker, the managing director of Dugout Ventures and a longtime financial adviser to Mr. Ortiz, said the principals had collectively invested more than $10 million in the venture. They plan to raise at least $50 million for investments in companies that Dugout’s athlete investors will support, endorse, and serve as expert consultants.

The nature of the players’ active involvement in the fund will make it unique, Mr. Walker said. The players plan to recruit active players to invest and serve as guinea pigs by testing equipment when Dugout is considering potential investments. In addition, the size of the players’ dividends from their investments will depend in part on how actively they support and endorse the products.

Retired sports stars have a mixed history as business titans. Kobe Bryant recently launched a $100 million technology fund to much fanfare, while Curt Schilling’s videogame company, launched 10 years ago, filed for bankruptcy in 2012.