Basic Marking

Marking is an active process, not a passive one. It involves reacting to whatever the thrower is doing to try to make any throw a more difficult one. The harder the marker works, and the better the mark, the less work defenders have to do to shut down their receivers.

So how do you put a good mark on a thrower? The following are general tips to improve your marking if you are not already doing them :

Keep on the balls of your feet.: You have to be able to react and move quickly, and this is not possible if you are back on your heels. You have much better balance if you are leaning slightly forwards.
Keep your weight low.: Crouch down, or at least bend your knees slightly. If you are marking well you should feel the effort in your quads. This allows you to get your hands low and also gives you much better balance.
Keep your hands low and arms spread.: This also helps your balance. Obviously though, if you are trying to prevent a high throw, that arm will have to be up. In general, the arm on the force side should always be as low as possible, since it is much harder to throw a good throw from higher up.
Learn to read fakes.: Many throwers make weak fakes without ever intending to throw. If you can pick these up, you will not be sucked in to following them and leaving an easy throw open.
Don’t overcommit on the open side.: It is not your job to block an open side throw. That is the defenders’ responsibility. If you let the thrower break because you tried too hard to block an open side throw, that is your fault.
Call "Up!" loudly when the thrower throws.: This allows the defenders to glance around to see where the disc is, since they will otherwise be watching the receivers. If the throw is hucked, call "Up long", to allow the people marking the opposing deep players time to see the disc.