To make extra money, he would engage in battle royales, which consisted of five to ten boys, usually Black, fighting each other, often blindfolded, until only one remained standing.
He quickly befriended some of the club's members, including golfing legend Bobby Jones, who helped fund his boxing training.
During this period, he earned his reputation as a relentless and powerful fighter, essential traits that endeared him to his fans and won over admirers.
In November 1942, he found himself in a fight against Allie Stolz at Madison Square Garden to determine who would challenge for the New York version of the world lightweight title.
[3][7] In his first NYSAC Lightweight Title bout against Tippy Larkin on December 18, 1942, Jack surprised again by knocking out the champion in the third round with a right uppercut to the chin.
The bout was furious and both boxers landed constant blows, though Jack seemed to withstand the onslaught of Larkin and deliver an equal or greater number of counterpunches.
[8] Jack twice defeated Fritzie Zivic at Madison Square Garden on February 5, and March 5, 1943, in ten and twelve round unanimous decisions, though their second meeting was rather close.
[10] Jack held the World Lightweight Title for only six months before dropping it to fellow hall-of-famer Bob Montgomery on May 21, 1943, before 18,343 in a fifteen-round unanimous points decision at the Garden.
But Montgomery quickly settled down and scored frequently with a strong straight right that at times had Jack close to a knockout and against which he could find no adequate defense.
[11] Jack would go on to regain the title from Montgomery on November 19, 1943, in a fifteen-round unanimous decision at New York's Madison Square Garden before a crowd of 17,866.
[3][4] Beau carefully followed the advice of his trainer Larry Amadee, who told him to stay close to Montgomery, fight fiercely when separated from clinches, and generally use his strength in infighting.
[13] Jack met Sammy Angott in a non-title match on January 28, 1944, drawing in ten rounds at Madison Square Garden before an impressive crowd of 19,113, the largest of the year.
[citation needed] Angott had a problem from a thigh injury he had received in training and was limping as he was led from the ring at the end of the bout.
[14][15] Jack finally lost the Lightweight Championship for the second time to Montgomery on March 3, 1944, in a fifteen-round split decision before 19,066 fans in Madison Square Garden.
[16] On March 17, 1944, he defeated Al "Bummy" Davis, the "Brooklyn Bomber", at Madison Square Garden before a crowd of nearly 20,000, in a ten-round unanimous decision.
[17] On March 31, 1944, Jack defeated Mexican-born boxer Juan Zurita in a ten-round points decision at New York's Madison Square Garden.
Jack took the fight on points after 10 rounds, however the highlight of the evening was when the lights dimmed and a spotlight shone on Joe Louis was standing in the front row.
[22][23][24] Jack would not challenge for the title again until July 12, 1948, when he fought hall-of-famer and reigning champion Ike Williams in a sixth-round TKO at Shibe Park in Philadelphia.
[25] Williams was managed and on occasion financially exploited by boxing promoter Frank "Blinky" Palermo, who was Mafia-connected and a partner of Murder Inc. button-man Frankie Carbo.