So as they travel to Chelsea on Sunday to face some of the best headers the league has to offer in Didier Drogba, John Terry and Ricardo Carvalho, Sportsmail talks to Anfield legend Phil Thompson about the pros and cons of zonal and man-to-man marking and how each one works.
Attacking threat: Chelsea's Didier Drogba will hope to take advantage of Liverpool's zonal marking system
MAN-TO-MANHow does it work? The five or six best headers of the ball pick up the biggest attacking threats on the opposing team and mark them tightly, following their runs. The defender must get to the ball ahead of the attacker and he is to blame if his man scores. There is also usually a man on each post, one on the edge of the box and one in front of the near post.
Phil says: Many years ago, everybody was man-to-man marking. When I was at centre back with Emlyn Hughes, I would take the biggest one of their players. Then the rest of them would mark whoever else was in the box. That way we never had any debate in the dressing room about accountability.
In my coaching times at Liverpool under Gerard Houllier, I would designate on the teamsheet who all players would mark. I'd list the players in order of the best headers of the ball and they would pick up a player.
I don't think there are too many flaws. The ideal thing about it is you get close to the player and make it as difficult as possible for him to get a run on you. People can get away from you, steal a yard and they will have a chance to attack the ball. It is each player's responsibility and they are happy with that. There is accountability if it goes wrong.
One downside is people often block off markers, which can cause trouble. In my time there, we had the best defensive record in the league for two or three seasons using man-to-man.
ZONALHow does it work? The defenders mark key areas of space rather than a man. There are usually three players standing along the six-yard box and three in front of them. There are also men on the posts and two between the set-piece taker and the near post. Players must not move from those positions, no matter where opposition players run.
Phil says: Managers choose it because they think they are covering all the major areas. For me, the biggest flaw is players don't have accountability. You can come in after a game and someone's scored from a set piece and everyone can shrug and say: 'It's not my fault.'
The other thing is you can have attackers running at you when you're standing still. They can be 5ft 2in, get a run on you and you could have five Sami Hyypias and you couldn't stop them. So when you get Didier Drogba or John Terry or Ricardo Carvalho coming at you with that momentum, you don't stand a chance.
But it's not just Liverpool using it. Some teams even do one type of marking for corners and another for free kicks. That's a lot for players to get their heads around.
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