The Jersey Flegg Cup began in 1961 as an under-19 age group competition and was originally played over 9–12 weeks early in the season, alongside the SG Ball Cup and Harold Matthews Cup during the NSWRL's junior representative season. In 1998, with the advent of the National Rugby League, the competition switched to the current under-20 age limit and was played over a full season, running alongside the senior NRL competition and culminating with the Grand Final held on the same day as the NRL Grand Final. The competition ceased at the end of the 2007 season to make way for the NRL-administered under-20 competition, the National Youth Competition, which commenced in 2008. In 2016, the NRL announced that the National Youth Competition would be discontinued after the 2017 season, in favour of state-based under-20 competitions, administered by the Queensland Rugby League and New SouthWales Rugby League. On 1 February 2018, the NSWRL officially announced the reintroduction of the Jersey Flegg Cup for the 2018 season after a 10-year absence.
The Jersey Flegg Cup follows the same regular season format as the Intrust Super Premiership, with games usually played as curtain-raisers to the senior fixtures. Beginning in early March, a round of regular season games is then played almost every weekend for twenty-one weeks, ending in late August. Unlike the Intrust Super Premiership, the Jersey Flegg Cup features three full rounds where every team receives a bye. These rounds are scheduled in to accommodate university exam periods. Teams receive two competition points for a win, and one point for a draw. The bye also receives two points; a loss, no points. Teams on the ladder are ranked by competition points, then match points differential and points percentage are used to separate teams with equal competition points. At the end of the regular season, the club which is ranked highest on the ladder is declared minor premiers.
Finals series
The eight highest placed teams at the end of the regular season compete in the finals series. The Jersey Flegg follows the same finals format as the NRL and the Intrust Super Premiership. The system consists of a number of games between the top eight teams over four weeks in September, until only two teams remain. These two teams then contest the Grand Final, which is played in late September at a suburban Sydney stadium, as a curtain-raiser to the Intrust Super Premiership Grand Final.