Seldin's nickname is the Hebrew Hammer. He is trained and managed by Pete Brodsky, and promoted by Joe DeGuardia. Seldin wears a
Star of David on his trunks, as did former Jewish boxers
Benny Leonard and
Barney Ross. Seldin began boxing as a professional in 2011, when he was 25 years old. The fight ended as a "
no-contest" in the third round, as the ringside physician called the fight when Seldin head butted Jargal and caused a badly swollen-shut right eye. In December 2014, he again faced Jargal. Seldin defeated him by a
technical knockout in the ninth round, winning the
World Boxing Council International Silver
Light Welterweight () title. He won with a technical knockout against Johnny Garcia (19–2–1, 11 KOs) on ESPN's
Friday Night Fights on February 27, 2015, headlining as the
main event in a fight for Seldin's WBC title. The referee stopped the fight in the fifth round. On June 20, 2015, Seldin defended his WBC International Silver junior welterweight title and brought his record to 17–0 with 14 knockouts, with a 4th-round main event TKO of Ranee Ganoy, who was 38-13-2 with 32 knockouts, at The Paramount. On April 6, 2017, Seldin tested positive for anabolic steroid use for a second time showing an increased level of testosterone and anabolic steroid Stanozolol also known as Winstrol, which forced his June 15 fight to be canceled. His testosterone to
epitestosterone ratio (T/E) was 21.02 to 1, which far exceeded the allowable threshold of 4 to 1 under World Anti-Doping Agency standards. The WBC ruled that Seldin was suspended from participating in any WBC-sanctioned bouts for six months, or until Aug. 1, 2017, and that VADA would design a specific random testing protocol for Seldin at his own cost that would go on for one year. On November 11, 2017, Seldin made his HBO Boxing debut fighting and winning in a third-round TKO against Roberto Ortiz, resulting in Ortiz's second-ever loss. Seldin's record improved to 21–0 with 17 knockouts. He is the reigning Super Lightweight Champion of the North American Boxing Association; in 2020 he broke his own record by winning 25 of 26 fights, with 21 knockouts, when he fought Luis Florez. On October 16, 2021, in the main event at TrillerVerz at
Barclays Center in Brooklyn, NY, he knocked out Brazil's
Willam Silva in the seventh round. ==Personal life==