At 14, Jack quit school to work as an electrician's helper in a Pittsburgh mill for three dollars a day, an attractive sum in that era.

[6] In one of his last amateur bouts on July 12, 1921 with Artie Martin at the New York Athletic Club, he received a shoulder injury that required surgery and caused him problems throughout his boxing career.

[8] Zivic defeated top rated contender Charley White in an upset on June 11, 1923 in a ten round newspaper decision at Motor Square Garden in Pittsburgh, Pennsylvania.

[9] He lost to the exceptional future world welterweight champion Joe Dundee on September 12, 1923 in a twelve round points decision in Baltimore.

[13] In an interview in 1960, Zivic said he believed he had made a decisive tournament win in defeating Barbarian, and indeed the New Castle Herald wrote that the win earned him the right to face Leonard for the title, but in fact several additional rounds would be required to take the world title, and Zivic had the misfortune to face a reigning champion in the next round.

[15][8] Bernstein, in his characteristic crouch, would rush into close quarters and then fire short, fast, rights and lefts to the head, keeping Zivic dazed and off balance.

[16] In what was likely his most notable win, he knocked out the exceptional lightweight contender Lew Tendler, now fighting as a welterweight, in a fifth round technical knockout at Motor Square Garden in Pittsburgh on January 19, 1925.

[8] In their May, 1926 meeting at Madison Square Garden, before a packed house of 20,000, Harmon may have taken the seventh, eighth, and ninth, but the fierce display in the final round, with both boxers looking evenly matched, likely convinced the referee to rule for a draw.

[19] Zivic lost to highly rated welterweight Sargeant Sammy Baker on July 2, 1929 in a brutal ten round points decision at the Meyers Bowl at North Braddock, Pennsylvania.

[8] Zivic met fellow Olympian and future world welterweight champion Jackie Fields on June 26, 1928, losing in a seventh round technical knockout at Olympic Auditorium in Los Angeles.

A right hook and left to the stomach, followed by a rain of blows while Zivic was on the ropes, forced the referee to end the bout in the seventh.

[23] Zivic lost much of his boxing investments in the 1929 stock market crash, but took a job with a local Pittsburgh area Post Office in 1934.

These included a shoeshine glove that dispensed black or tan polish, a towel that had separate sections for body and face, a tool to pry hubcaps, and a plexiglass license plate.