Juan Sebastián Boselli Graf (born 4 December 2003) is a Uruguayan professional footballer who plays as a defender for Argentine Primera División club River Plate. Boselli was born on 4 December 2003 in Montevideo, Uruguay to Pablo Boselli and Erika Graf. Many of his relatives are professional athletes; Pablo is a former padel player who captained the Uruguay national padel team in the 2008 Padel World Championship. He currently works as a football agent. Erika is a professional swimmer who competed in the 1996 Summer Olympics. His older brothers, Juan Martín and Juan Manuel, are also professional footballers, the latter of whom has also represented Uruguay on the international stage. Boselli is of paternal Italian descent and holds an Italian passport, whereas his mother is of German heritage. Boselli is a youth academy graduate of Defensor Sporting. He made his professional debut for the club on 7 September 2022 in a Uruguay Cup 1–0 victory against Racing Club de Montevideo. His team subsequently ended up winning the competition. On 23 August 2023, an agreement was announced by River Plate to sign Boselli. The unveiling was published on River Plate's social media platforms on 29 August. Boselli made his official debut with the club on 9 December against Rosario Central in the semifinals of the 2023 Copa de la Liga Profesional, but would lose on penalties. On 22 December, he was once again called for the starting lineup in a rematch against Rosario Central, this time for the 2023 Trofeo de Campeones de la Liga Profesional. Boselli played the whole match and was praised for his performance; River eventually won 2-0 for their 71st title. Boselli is a Uruguayan youth international, most notably being one of the standout players of the Uruguay national under-20 football team in the 2023 South American Youth Championship. He was then a part of the Uruguayan side that won the 2023 FIFA U-20 World Cup in Argentina. In June 2023, Boselli received his first call-up to the senior team for friendlies against Nicaragua and Cuba. In January 2024, he was named in Uruguay's squad for the 2024 CONMEBOL Pre-Olympic Tournament under Marcelo Bielsa.