New York Times:
[A] sock is the team symbol again, only this time it is a five-toed version popularized by their two new Japanese pitchers – Daisuke Matsuzaka and Hideki Okajima.
The socks, which fit like a glove with each toe individually encased, were met with curiosity in Boston's clubhouse during spring training. Before long, Matsuzaka began offering pairs to anyone who expressed an interest. And a number of players did, including Mike Lowell, Alex Cora and Doug Mirabelli, who are now playing in them regularly. ...
The socks that Matsuzaka wears are covered with tiny rubbery beads on the sole for better traction. As for Okajima, he said the individual toe slot helps with his balance because he can firmly grip each toe. ... "They give me a better feel and perception of the ground, a sensitivity similar to bare feet," Matsuzaka said.
Matsuzaka has been wearing the five-toed socks since he signed his first professional contract in 1999, with the Seibu Lions of Japan's Pacific League. The socks are popular among professional baseball players in Japan and versions of them are also common among the general public in Japan.