For questions about Magic: The Gathering's Competitive REL (Rules Enforcement Level), used at major tournaments and competitive events (for example Pro Tour Qualifiers and Grand Prix Day 1).
The Competitive Rules Enforcement Level (REL) for Magic: the Gathering is the level of rules enforcement used for most Magic tournaments above the Friday Night Magic level, including Grand Prix Day 1s and Pro Tour Qualifiers. This REL expects players to have a good knowledge of game rules and tournament procedures and has stricter rules enforcement than Regular REL. The official definition can be found in the Magic: the Gathering Tournament Rules.
Not all Magic: the Gathering questions need a Rules Enforcement Level tag. Questions using this tag should be about how tournament or other high-level Magic play under the Competitive REL affects the various parts of the game, especially judge rulings and player interactions.