There is no actual "man marking" in FM. Except if you specifically set a player to mark a specific player in the drop-down list. Only in that case will the player stick to the man wherever he will go when your team is defending (not in possession).
Marking: Marking options are difficult to explain in real world concepts because Football Manager as yet has not quite sorted out the real mechanics of the system. Essentially, zonal marking strategies will look to mark the opposition player who comes in to the player’s “zone” on the field. Man marking strategies mean that each player is assigned a particular person to mark.
In Football Manager, however,
man marking tends to be a more aggressive zonal marking system, whereby a player will stick to the man who enters his zone, but stay with him until the danger is cleared. The best advice with marking is to experiment with which settings work best. For more in-depth analysis of the inner-workings of Football Manager’s marking, please refer to future Tactical Bible articles.
True, real life man-marking is actually “specific” marking, which can be set before or during the upcoming match, either by manually setting the marking settings for an individual player or by using opposition instructions to target certain individuals.