RFU Regulation 15.12.
The Half Game Rule
1. Other than as set out in RFU Regulation 15.12.2, all Clubs & Teams must ensure that each player selected in every match day squad plays at least half of the Available Playing Time.
This requirement is mandatory across the entire age-grade game and in respect of all contact and non-contact age-grade matches, including 7 a-side matches and festivals/tournament matches.
2. In respect of the U18 Academy Competition only, all Clubs must ensure that each player selected in every match day squad plays at least 20% of the Available Playing Time.
3. Available Playing Time means the total amount of playing time available to a team on any particular day. Where a team is participating in multiple matches in one day, the total available playing time will be the total number of minutes across all matches played by the team on that day; and in all cases (a) includes playing time spent off the pitch due to a temporary injury or yellow card and (b) excludes playing time that would have been available had a match not be abandoned or shortened due to bona fide reasons or in accordance with Regulation 15.11.3.
4. Regulation 15.12.1 will not apply in the event that a player is permanently removed from the match:
a) due to an injury incurred during the match;
b) as a result of a bona fide risk of injury; or
c) as a result of a red card or in the event of the Referee requesting that a player be permanently removed from the match.