His four-year-old season commenced with a win in the San Fernando Stakes. Another quarter crack developed in Buckpasser’s off (right) fore hoof, and he did not race for 4½ months. When he returned, he scored his 15th consecutive victory in the Metropolitan Mile. On June 17, 1967, Buckpasser's winning streak ended with his first and only attempt at racing on grass. He finished third to stablemate Poker in the Bowling Green Handicap at Aqueduct Racetrack. Assagai, the 1966 turf-course champion, finished second. As "The Blood-Horse" said in its July 24, 1967, issue: "Never had so many people had so many immunization shots in order to stay home and watch the Suburban Handicap on Independence Day." Three reasons were advanced for his defeat: turf, shoes, and weight. Buckpasser also ran that day with his head held in an uncommon way, slightly sideways. No one has ever understood why.