A minigame can take over a player's sidebar for the length of a match and hand it back afterwards. Compile against the jar, soft-depend on Scoreboard-OG, and only touch the API after checking the plugin is enabled.

import plugin.api.ScoreboardOGAPI;
import plugin.api.SidebarProvider;

ScoreboardOGAPI.claim(player, "MyGame-OG", new SidebarProvider() {
    public Component title(Player player) { return Component.text("My Game"); }
    public List<Component> lines(Player player) { return List.of(Component.text("Players: 4")); }
});
// later
ScoreboardOGAPI.release(player, "MyGame-OG");
// on disable
ScoreboardOGAPI.releaseAll("MyGame-OG");

claim replaces the network board with the provider's content, polled on the main thread every ten ticks; up to 15 lines, fewer lines shrink the board. release hands the sidebar back only when the named owner still holds it, and the network board returns on its own. A player who hid the sidebar with /togglescoreboard sees neither board. A provider that throws loses its claim.

TheHerobrine-OG, BuildBattle-OG and Splegg-OG use this API and fall back to their own scoreboards when Scoreboard-OG is absent.

Scoreboard-OG is public domain software released under the terms of The Unlicense.