[5] Occasionally, during his junior and senior years of high school he also played both sports for the University of Minnesota, where he was a catcher in baseball and a halfback in football.

[8] According to Corbin, during Heffelfinger's first year, in spite of his skill, the freshman from the Midwest was not sufficiently ferocious for the Yale style of play until Howard Knapp, one of the graduate coaches, motivated him by an unusual method: The freshman Heffelfinger was 6 feet 3 inches in height, weighed 210 pounds and looked like the most demure, gentle, self-effacing individual that could be imagined.

His usual posture was head bowed, shoulders stopped, eyes to the ground, with no idea whatever of his marvelous power and nature-given ability to strike terror in his opponents.

Heff found himself that day and from then on was a terror to his opponents.The 1888 Yale team was not only undefeated and untied, but unscored upon, with a season scoring record of 698 to 0.

His teammates included, besides Pa Corbin: Alonzo Stagg, Charley Gill, Billy Rhodes, Lee "Bum" McClung and George Washington Woodruff.

"[11] Heffelfinger's athletic activities at Yale were not limited to football: he lettered in three other sports: rowing, baseball and track,[11] and won the university heavyweight boxing championship.

[12] After leaving Yale, Heffelfinger played amateur football for the Chicago Athletic Association (for which he was compensated with "double expenses", as was a common practice at the time).

[7][14] In the 1960s a man known only as "Nelson Ross" walked into the office of Art Rooney, the president of the Pittsburgh Steelers of the National Football League.

Ross' examination of Pittsburgh newspapers indicated that the first pro American football player actually was Pudge Heffelfinger, an all-American guard from Yale, who was hired to play for Allegheny on November 12, 1892, for $500 (equivalent to $16,956 in 2023).

The Pro Football Hall of Fame soon discovered a page torn from an 1892 account ledger prepared by Allegheny manager, O. D. Thompson, that included the line item: "Game performance bonus to W. Heffelfinger for playing (cash) $500.

[1] The week after the game against the P.A.C., Allegheny paid former Princeton end Ben "Sport" Donnelly $250 to play alongside Pudge against Washington & Jefferson College.

[21] After the failure of the manufacturing business, Heffelfinger had an active career in real estate,[12] including major commercial deals.

[22] In his real estate work, Heffelfinger is credited with important contributions to the early development of the upper Nicollet Avenue area, with organizing the company which built the 1910 Physicians and Surgeons building, and with bringing Butler Brothers to Minneapolis.

[12] He first won elective office in 1924, running against more experienced politicians and easily capturing a seat on the Hennepin County Board of Commissioners.

[12] During Prohibition Heffelfinger ran twice as a "wet" in the Republican primary for Minnesota's 5th congressional district, losing both times to prohibitionist and former Lieutenant Governor William I.