The first was in his seventh fight when he was knocked out by Joe Chip, who heavily outweighed him; the second happened two years later when Greb broke the radius of his left arm against Kid Graves.

[citation needed] In 1921, during a fight with light heavyweight Kid Norfolk, he was thumbed in the right eye, which is believed to have resulted in a retinal tear.

It is commonly believed that Greb completely lost sight in the eye after his fifth bout with Bob Roper, after which it took almost two months to recover.

In the first round, Greb immediately fractured Tunney's nose in two places and then proceeded to open a deep gash over his left eye.

According to eye-witness reports, Greb was subsequently forced to intermittently commission the referee to wipe off his bloodstained gloves with a towel.

Throughout the bout, Greb would repeatedly petition the referee to stop the fight while a determined Tunney concurrently implored him to allow the contest to continue.

In a hotly disputed battle at Madison Square Garden in February 1923, Tunney regained his title by a highly controversial split decision.

Multiple eyewitness reports state that Greb controlled the fight and battered Tunney, cutting and rocking him from punches on more than one occasion.

Tunney reputedly consented to this request and later acknowledged the incident as the highest tribute he received in his career, stating, "Here was one of the greatest fighters of all time laying down his shield, admitting defeat and knowing I would not expose him."

[11] One month after losing his light heavyweight title to Tunney, Greb set his sights on middleweight champion Johnny Wilson; however, when Wilson's manager Marty Killelea refused to offer him the bout, Greb paid a few speakeasy servers in Pittsburgh and New York to serve him water in coloured tumblers and then feigned intoxication in a highly theatrical spectacle.

Greb's most notable defense of the title was against the reigning world welterweight champion, Mickey Walker, in July 1925 at the Polo Grounds in New York.

The middle rounds saw Greb starting to relax and control the pace of the bout while Walker could still land some eye-catching combinations.

[14] At 32, a waning Greb was years past his best when he was matched with tricky southpaw Tiger Flowers (who was 31 at the time) in Madison Square Garden in February 1926.

[4] Flowers beat Greb again in their rematch six months later, on an even more controversial decision, the fans storming the ring to protest the outcome.

[15] Greb retired following the second Flowers loss and relayed to a friend that he planned on opening a gym in downtown Pittsburgh.

Nobody can get him in good enough condition to whip Gene"), Greb checked into an Atlantic City clinic for surgery to repair damage to his nose and respiratory tract caused by his ring career and several car crashes.

Greb was willing to box African-American fighters, including Jack Blackburn, Kid Norfolk and Tiger Flowers, in an era when many white boxers refused to do so.