An affiliate of Los Angeles private equity firm Leonard Green & Partners LP has agreed to buy Sports Authority Inc. for $1.3 billion and take the country’s largest sporting goods chain private.

The affiliate, Green Equity Investors IV LP, which includes current members of Sports Authority’s management team, will pay $37.25 per share in cash, a 20 percent premium on Friday’s $31.05 closing price. The deal is expected to close in the second quarter of this year.

“As a private company, Sports Authority will have greater flexibility to accomplish its long-term goals,” said Doug Morton, Englewood, Colo.-based Sports Authority’s chairman and chief executive, in a statement. “Leonard Green & Partners has an excellent track record of building value at its portfolio companies by providing strong financial and strategic support.”

Leonard Green is one of the nation’s largest private equity firms with about $3.7 billion of private equity capital under management. The firm has a history of making long-term investments, sometimes more than 10 years, in companies that are industry leaders.

Companies currently in Leonard Green’s investment portfolio include Internet florist FTD Group Inc., upscale retailer Neiman Marcus Group Inc., drugstore chain Rite Aid Corp., and map company Rand McNally & Co. Prior investments include pet supplies retailer PETCO Animal Supplies Inc. and Big 5 Sporting Goods Corp., another sporting goods chain.

Sports Authority operates nearly 400 stores in 45 states. After a 2003 merger with Gart Sports, the Sports Authority umbrella grew to include Gart Sports, Sportmart and Oshman’s Sporting Goods locations as well as its namesake stores.

Investors reacted positively to news of the acquisition. On Monday, shares of Sports Authority rose 18.2 percent to settle at $36.70.