Northrup declined offers to play quarterback for the Chicago Bears and New York Titans to sign with the Tigers. A classic streak hitter and one of Detroit's best in the clutch during the 1960s, he played right and center in a talented but crowded outfield
that included Al Kaline, Willie Horton, and Mickey Stanley. In their 1968 World Championship season, he led the Tigers with 153 hits and 90 RBI, and broke up three no-hitters in April and May. He hit four grand slams that year. Two came in consecutive at-bats
on June 24, and he added another on June 29 for three in one week, a ML record. He
hit yet another off the Cardinals' Larry Jaster in Game Six of the World Series.
His two-run triple was the crucial blow in Game Seven. On August 28, 1969 against
Oakland, he became the first Tiger since Ty Cobb to go six-for-six, finishing the
game with a 13th-inning home run over the Tiger Stadium roof. In 1973, he had a second
eight-RBI game, against Texas, and hit a career-high .307. Dealt twice in 1974, he
retired a year later.