[citation needed] He lettered in football in 1899, 1900, and 1901 and served as captain his senior year under coach J. J. Hazen.

The Williams College team that O'Neill captained had an overall record of 6–4 with losses to Harvard, Dartmouth, Columbia, and Army.

Even with those losses, the O'Neill-led team went on to win the 1901 Tricollegiante Football Association championship, with victories over league rivals Wesleyan and Amherst.

After 1915, the year O'Neill founded his law practice in New York City, he had to cut back on his coaching duties.

In his last game at Columbia, he suffered one of the worst losses in his career, a 59–6 blowout to his old school, Colgate, on Thanksgiving Day.

[6] In 1902, O'Neill resurrected the Syracuse Athletic Club, to take part in the 1902 World Series of Football, held at Madison Square Garden.