GROUP BY count?

I am having trouble grouping by the row count when using find() instead of count().

$players = self::find([
        'winnerId IS NOT NULL AND completed IS NOT NULL AND completed > :date:',
        'bind' => [
            'date' => new \Phalcon\Db\RawValue('DATE_SUB(NOW(), INTERVAL 1 MONTH)')
        ],
        'group' => 'winnerId',
        'order' => 'rowcount'
]);