Marking

A Mark is taken if a Player catches or takes control of the football:

(a) within the Playing Surface; and

(b)after it has been Kicked by another Player a distance of at least 15 metres; and

(c) which has not touched the ground or been touched by another Player during the period when the football was Kicked until it was caught or controlled by the Player.

(a) For the avoidance of doubt, a Mark shall be awarded if:

(i)  a Player catches or takes control of the football before it has passed completely over the Boundary Line, Goal Line or Behind Line;

(ii) before the football was caught or controlled by the Player, it was touched by an Umpire or any other Official.

When a Player has taken a Mark, the field Umpire shall award the Mark to the Player at the location on the Playing Surface where the Mark was taken.

If a field Umpire incorrectly blows the whistle to award a mark that was not subsequently completed, they may cancel the decision and call “Play On”.

If the Player retains possession of the football, and the Player is correctly tackled by an opponent, the field Umpire shall call a ball up provided the field Umpire is satisfied that the Player could not reasonably have disposed of the football.

Standing the Mark

When a Player is awarded a Mark or Free Kick or is Kicking into play after a Behind has been scored, one Player from the opposing Team may stand at the position on the Playing Surface where the Mark or Free Kick was awarded or where the field Umpire otherwise directs the Player to stand. The position on the Playing Surface where the opposing Player stands is known as “the mark”.

Protected Area

The Protected Area is a corridor which extends from 5 metres either side of the mark to 5 metres either side of, and a 5-metre radius behind, the Player with the football. No Player shall enter and remain in the Protected Area unless the field Umpire calls “Play On” or the Player is accompanying or following within 5 metres of their opponent

A Player who has been awarded a Mark or Free Kick shall dispose of the football from directly behind the mark. If a Player disposes or attempts to dispose of the football other than in a direct line over the mark, the field Umpire shall call “Play On” and the football shall immediately be in play.

Kicking for Goal from a Mark

(a) Where a Player is Kicking for a Goal after being awarded a Mark or a Free Kick, the Kick shall be taken along a direct line from the mark to the centre of the Goal Line.

(b) If your mark is taken in the “goal square” the Kick shall be taken from directly in front of the Goals from a spot horizontally across from where the Mark or Free Kick was awarded.

Encroaching on the Mark

If the Player standing the mark encroaches the mark whilst a Player is in the act of Kicking for Goal, the following shall apply:

(a) if a Goal is Kicked, the field Umpire shall signal “All Clear” and a Goal shall be recorded; and

(b) if a Goal is not Kicked, the Player may elect to take another Kick, in which case the Player shall also be awarded a Fifty-Metre Penalty.

http://www.afl.com.au/video/2016-03-17/2017-laws-of-the-game-marking-contest