Harper played at Encinal High School in Alameda, California,[1] where his teammates included future Baseball Hall-of-Famer Willie Stargell and MLB player Curt Motton.

[4] Harper was the first player to come to bat in Seattle Pilots history when he led off the top of the 1st against right-hander Jim McGlothlin of the California Angels.

[3] He also became the first Brewer, and just the fifth major leaguer at that point, to join the 30–30 club by hitting 31 home runs and stealing 38 bases and came in sixth in the AL MVP voting.

[7] Harper was part of a ten-player blockbuster that sent him, Marty Pattin, Lew Krausse and minor-league outfielder Pat Skrable to the Boston Red Sox for George Scott, Jim Lonborg, Ken Brett, Billy Conigliaro, Joe Lahoud and Don Pavletich on October 10, 1971.

[8] Harper became the Sox' starting center fielder and leadoff hitter from 1972–74, playing well enough to earn him votes in the AL MVP balloting in '72 and '73.

[3] 1973 was his best season with the club, as he led the league in stolen bases for the second time in his career, setting an all-time Red Sox mark with 54, until Jacoby Ellsbury broke the record on August 25, 2009.

[3] Harper's trade to the California Angels for Bob Heise at the Winter Meetings on December 2, 1974 was driven by the Red Sox using its outfielder surplus to address its lack of infielder depth.

[3] Revitalized by the trade to a contender, Harper hit .319 in August and September for the A's and became their starting first baseman, also seeing spot duty in the outfield and at third base.

Harper finally saw his first playoff action at age 34 after 14 major league seasons, but was limited to one plate appearance, a walk, as the A's were swept by his old team, the Red Sox.

[11] On July 1, 1986, the Equal Employment Opportunity Commission vindicated Harper and cited the Red Sox for illegal actions.