The new rule, which was trialled in the 2009 and 2010 NAB Cup competitions, will allow clubs to introduce their substitute into games at any time, but the player who is replaced cannot return to the field.
"Interchange numbers per club have doubled from an average of 58 per game in 2007 to 117 per game in 2010," AFL football operations manager and chairman of the laws of the game committee Adrian Anderson said.
The AFL has cited three reasons - congestion, fairness and injuries - for changing the interchange rules for the first time since the fourth bench player was added in 1998.
"The use of interchange has created more congestion, more stoppages, more defensive pressure and has contributed to a drop in disposal efficiency," Anderson said.
"The laws committee was also concerned about the increasing effect of the interchange on match fairness.
"The interchange was originally designed to help teams when they had an injury, but was increasingly a disadvantage to a team with an injury, because it was unable to rotate their players as much as the opposition.
"The medical advice was also telling us that a restriction should be applied to try to arrest the current injury trend."
Three different interchange rules were floated for discussion by the laws committee in August.
They were:
- three interchange players and one subtitute
- two interchange players and two substitutes
- four interchange players, with a cap of 80 interchanges per game
The laws committee subsequently chose to recommend the one-sub system to the league executive, which endorsed it. The new rule was then ratified by the AFL Commission.
The league has made two other changes for the 2011 season.
The advantage rule trialled in this year's pre-season NAB Cup competition, whereby the player not the umpire determines whether there is an advantage in playing on after a free kick, will be introduced.
In addition, the rule on head high bumps has been clarified.
A player who elects to apply a bump in any situation can now expect to be reported if he makes forceful contact with the head, unless:
- the player was contesting the ball and did not have a realistic alternative way to contest the ball
- the contact was caused by circumstances outside the control of the player which could not be reasonably foreseen.
The laws committee did not recommend any change to the game's scoring system, nor any change to the length of quarters.
The laws committee consists of Anderson, Kevin Bartlett, Luke Darcy, Andrew McKay, Leigh Matthews, Matthew Pavlich, Luke Power, Rowan Sawers and Michael Sexton.
