A small stake in the San Francisco Giants is for sale at a price that could value the team at about $4 billion, according to people familiar with the matter. The Major League Baseball team is owned by around 30 partners, including former catcher Buster Posey and investor Arctos Sports Partners. Charles B. Johnson, 91, a former chief executive officer of Franklin Templeton Investments, holds the largest stake at about a quarter. The stake is less than 5% and related to estate planning, the person said, who asked not to be named discussing private information.