Often discussed on the web but never really solved.

This is my solution to enable inter-group/non-conference/across-groups matches in the LeagueManager WordPress Plugin.

You have to customize the plugin source a bit.

Open the file wordpress/wp-content/plugins/leaguemanager/admin/match.php and disable following line of code:

if ( $is_finals ) {
$teams = $championship->getFinalTeams($final);
} else {
$search = "league_id = '".$league->id."' AND `season`  = '".$season['name']."'";
if ( $cup ) {
//$search .= " AND `group` = '".$group."'"; //comment this line here using 2 frontslashes
}

Upload and replace the file. Now you should be able to assign Home and Guest Teams across groups with your Championship.