use get_stylesheet_directory() instead of get_template_directory()

In lib/shortcodes.php, you should be using get_stylesheet_directory or your template files won’t work with child themes. get_template_directory always returns the parent theme.

function loadTemplate( $template, $vars = array() )
        {
                global $leaguemanager, $lmStats, $championship;
                extract($vars);

                ob_start();
                if ( file_exists( get_stylesheet_directory() . "/leaguemanager/$template.php")) {
                        include(get_stylesheet_directory() . "/leaguemanager/$template.php");
                } elseif ( file_exists(LEAGUEMANAGER_PATH . "/templates/".$template.".php") ) {
                        include(LEAGUEMANAGER_PATH . "/templates/".$template.".php");
                } else {
                        parent::setMessage( sprintf(__('Could not load template %s.php', 'leaguemanager'), $template), true );
                        parent::printMessage();
                }
                $output = ob_get_contents();
                ob_end_clean();
                return $output;
        }

https://wordpress.org/plugins/leaguemanager/