He simultaneously worked as a navy boxing instructor, as did his friend boxer Mel Coogan, before he was discharged and returned to his civilian amateur career.

His patriotic service in World War I and subsequent training and participation in the Olympics delayed his entry into boxing's professional ranks until he reached the age of twenty four.

Not long after the opening bell, Mosberg feinted, and connected with a powerful hook to Beland's chin that sent his opponent to the canvas for the count and ended the bout.

[1] In his first professional match, on December 7, 1920, Mosberg defeated Frank Cassidy, in a close ten-round newspaper decision of the Philadelphia Record at the Fourth Regiment Armory in New Jersey.

The boxing card included Mosberg's friend and future lightweight contender Mel Coogan against Jewish boxer Eddie Wallace.

[14] Edwards, a quality journeyman featherweight, had met Patsy Cline, Johnny Clinton, and Joe Tiplitz, but he was on the downside of his career, and had not amassed an impressive record against the contenders he had faced.

[6] Facing even stiffer competition on February 5, 1921, Mosberg knocked out top lightweight contender Frankie Conifrey in the second of twelve rounds.

Conifrey had dislocated his shoulder in the second after aiming a left at Mosberg that missed, and the referee had to call the bout off to allow a doctor to treat the injury.

[16] Earlier in January, 1921, Conifrey had defeated Mosberg at Madison Square Garden, the shrine of East coast boxing, in a six-round split decision.

[6] Mosberg lost to his friend, highly rated lightweight contender, Mel Coogan on August 13, 1921, before a large crowd at Long Island's Queensboro Stadium in a twelve-round points decision.

Coogan, who had risen in the ranks to a well-rated lightweight contender, beat his old friend easily, though he knew his style and technique from their years of coaching navy boxers together in World War I.

Pryel would fight several highly rated lightweights in his later career including Ever Hammer and Jewish boxer Joe Tiplitz, but have a spotty record against them.

The fast and close contest featured a great deal of clinching, that kept the referee busy separating the wary combatants who knew the skills of their opponent from their previous fight.

[29] On June 26, 1922, Mosberg was knocked out a few seconds into the first round by southpaw Eddie Fitzsimmons in an important twelve-round, semi-final match before a huge crowd of 20,000 at New York's Bronx Velodrome.

The powerful Fitzsimmons had beaten future world Junior Welterweight champion Pinky Mitchell and had fared well against the great lightweights Johnny Dundee, Pal Moran, and New York Jewish battler Lou Tendler.

[6] Near the end of his career on August 14, 1923, Mosberg had a close ten-round fight with Jack Rappaport at the open air arena of Broad Athletic Club in Newark, New Jersey.

Mosberg suffered from a six-inch disadvantage in height, greatly limiting his reach against Rappaport but won the bout in the decision of the New York Evening Telegraph, who wrote "Sammy had a clear lead over his opponent all the way".

[31][32] In his last reported bout, on October 8, 1923, Mosberg lost to local boxer Jack McFarland in a close eight-round points decision at Dreamland Park in Newark, New Jersey.

He knew that the recent death of his manager Jack Bulger would impede his chance to find future matches, and he was drawn to the opportunity to go into the furniture business with his father.