Kazuo Matsui is still playing baseball. Better known simply as Kaz, the second baseman is playing in the Nippon Professional Baseball league which is the highest league in Japan. He plays for the Tohoku Rakuten Golden Eagles, since 2011.
This is the same league Matsui got his start in professional baseball in 1995 with the Seibu Lions. He was an excellent player in Japan and the Mets signed him as a shortstop in 2004 when he was 28. Matsui struggled in 2005 after a decent rookie season in the majors. His second season he batted .255 in only 87 games.