SET @anzahl=0;
SELECT IF(Sieg=1, @anzahl:=@anzahl+1, @anzahl:=0) AS Serie FROM (
    SELECT e.datum, t.teamname, m.tore_heim, m.tore_gast,
        IF(m.team_heim_id = t.team_id, 
          IF(m.tore_heim > m.tore_gast, 1, 0), 
          IF(m.tore_heim < m.tore_gast, 1, 0)
       ) AS Sieg
    FROM teams t 
    INNER JOIN matches m ON (m.team_heim_id = t.team_id OR m.team_gast_id = t.team_id) 
    JOIN eintraege e ON e.eintrags_id = m.eintrags_id 
    WHERE t.team_id = 12
    ORDER BY e.datum DESC
    ) AS temp

CREATE TABLE IF NOT EXISTS `eintraege` (
  `eintrags_id` int(11) NOT NULL AUTO_INCREMENT
  `bemerkung` varchar(32) DEFAULT NULL,
  `datum` datetime NOT NULL DEFAULT '0000-00-00 00:00:00'
  PRIMARY KEY (`eintrags_id`)
) ENGINE=InnoDB

CREATE TABLE IF NOT EXISTS `teams` (
  `team_id` int(11) NOT NULL AUTO_INCREMENT
  `teamname` varchar(75) NOT NULL DEFAULT ''
  PRIMARY KEY (`team_id`),
  UNIQUE KEY `teamname` (`teamname`)
) ENGINE=InnoDB 

CREATE TABLE IF NOT EXISTS `matches` (
  `match_id` int(11) NOT NULL AUTO_INCREMENT,
  `eintrags_id` int(11) NOT NULL DEFAULT '0',
  `team_heim_id` int(11) NOT NULL DEFAULT '0',
  `team_gast_id` int(11) NOT NULL DEFAULT '0',
  `tore_heim` int(3) NOT NULL DEFAULT '0',
  `tore_gast` int(3) NOT NULL DEFAULT '0',
  PRIMARY KEY (`match_id`)
) ENGINE=InnoDB 

INSERT INTO `eintraege` (`eintrags_id`, `bemerkung`, `datum`) VALUES
(1, '1. Spieltag 2010/11', '2010-08-19 14:46:08'),
(2, '2. Spieltag 2010/11', '2010-08-19 15:18:13'),
(3, '3. Spieltag 2010/11', '2010-08-19 19:07:17')

INSERT INTO `teams` (`team_id`, `teamname`) VALUES
(1, 'Team 1'),
(2, 'Team 2'),
(3, 'Team 3'),
(4, 'Team 4'),
(5, 'Team 5'),
(6, 'Team 6'),
(7, 'Team 7'),
(8, 'Team 8'),
(9, 'Team 9'),
(10, 'Team 10'),
(11, 'Team 11'),
(12, 'Team 12'),
(13, 'Team 13'),
(14, 'Team 14'),
(17, 'Team 15'),
(18, 'Team 16')

INSERT INTO `matches` (`match_id`, `eintrags_id`, `team_heim_id`, `team_gast_id`, `tore_heim`, `tore_gast`) VALUES
(1, 1, 1, 2, 2, 3),
(2, 1, 3, 4, 0, 1),
(3, 1, 5, 6, 5, 3),
(4, 1, 7, 8, 4, 3),
(5, 1, 9, 10, 1, 7),
(6, 1, 11, 12, 2, 1),
(7, 1, 13, 14, 4, 2),
(8, 1, 17, 18, 6, 1),
(9, 2, 14, 1, 2, 5),
(10, 2, 7, 10, 0, 0),
(11, 2, 2, 11, 2, 0),
(12, 2, 17, 9, 6, 0),
(13, 2, 12, 18, 6, 2),
(14, 2, 8, 3, 2, 1),
(15, 2, 4, 5, 5, 1),
(16, 2, 6, 13, 5, 0),
(17, 3, 9, 12, 4, 2),
(18, 3, 10, 3, 8, 1),
(19, 3, 5, 13, 2, 2),
(20, 3, 7, 17, 5, 1),
(21, 3, 2, 18, 10, 2),
(22, 3, 11, 14, 4, 2),
(23, 3, 4, 8, 0, 5)

SELECT
  t.teamname,
  MAX(COALESCE(e2.spieltag,4)-COALESCE(e1.spieltag,4)) AS seriendauer
FROM
  teams t
    LEFT JOIN (matches m1 LEFT JOIN eintraege e1 ON m1.eintrags_id=e1.eintrags_id)
      ON t.team_id IN(m1.team_heim_id,m1.team_gast_id)
         AND ((t.team_id=m1.team_heim_id AND m1.tore_heim>m1.tore_gast) 
             OR (t.team_id=m1.team_gast_id AND m1.tore_gast>m1.tore_heim))
    LEFT JOIN (matches m2 LEFT JOIN  eintraege e2 ON m2.eintrags_id=e2.eintrags_id)
      ON t.team_id IN(m2.team_heim_id,m2.team_gast_id) 
         AND e2.datum>e1.datum
         AND e1.saison=e2.saison
         AND ((t.team_id=m2.team_heim_id AND m2.tore_heim<m2.tore_gast) 
             OR (t.team_id=m2.team_gast_id AND m2.tore_gast<m2.tore_heim))
GROUP BY
  t.team_id,
  t.teamname

... MAX(COALESCE(e2.spieltag,4)-COALESCE(e1.spieltag,4)) AS seriendauer ...