Robert Edward Crosby (born January 12, 1980, in Lakewood, California) is an infielder in Major League Baseball who has played for the Oakland Athletics since 2003. The son of former major league infielder Ed Crosby, he bats and throws right-handed. He was Rookie of the Year in 2004.

Crosby attended La Quinta High School in Westminster, California alongside Detroit Tigers catcher Gerald Laird and California State University, Long Beach with New York Mets outfielder Jeremy Reed.

In 2004, his first full season, he took over the Athletics' shortstop duties from 2002 American League Most Valuable Player Miguel Tejada, who signed with the Baltimore Orioles as a free agent. That year, Crosby hit .239 with 22 home runs and 64 RBIs. He also led American League rookies in hits (130), doubles (34) and walks (58), and was third among AL players with 4.17 pitches per plate appearance. These numbers earned Crosby Rookie of the Year honors, the sixth Athletics player to do so after Harry Byrd (1952), José Canseco (1986), Mark McGwire (1987), Walt Weiss (1988), and Ben Grieve (1998).