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A push in the back is a free kick awarded in Australian rules football against a player who illegally tackles or interferes with a player from behind. The rule is applied in two different circumstances: tackles and marking contests.
Push in the Back: Tackle 
A tackler, loosely speaking, is not allowed to push an opposition player in the back during a tackle. By the strictest definition of a push, any contact from behind could be considered a push in the back, so the rule is usually enforced under only the following three circumstances:
- If a player is bent over or on his knees, usually to win or protect the football, and an opponent knocks him over from behind.
- If a player is lying face down on the ground, and an opponent falls onto his back, intentionally or unintentionally. The first circumstance often directly causes this second circumstance also.
- If a tackler pursuing a ball-carrier uses one or both hands to push him from behind, causing him to be knocked off-balance as he attempts to dispose of the ball. A chaser often attempts this when he sees that the ball-carrier is about to kick the ball, and he is not close enough for a tackle.
While the second and third circumstances are objectively applied by umpires, there is some subjectivity concerning the first interpretation. This arises because a bent-over player can be easily knocked over by incidental contact, forcing the umpire to make a judgement call regarding whether or not be considers the push to be sufficiently substantial to warrant penalty. Furthermore, it is not uncommon to see a player "take a dive" when he feels contact from behind, and umpires will not pay a free kick if they believe this to be the case. Nevertheless, it is relatively easy for fans to predict when these free kicks are going to be paid. Umpires are much less lenient if a player pushes another near the boundary line, due to the increased danger of crashing into the fence.
Push in the Back: Marking Contest 
One of the rules introduced by the VFL when they split from the VFA 1897 was the protection of a player who jumped for a mark from being put off balance by a player pushing him from behind. Pushes in the back are usually paid under the following three circumstances.
- If a player pushes an opponent who has jumped to take a mark.
- If a player on the lead is put off-balance by contact from behind with the arms of an opponent.
- If a player in a pack or standing one-on-one marking contest is pushed out from behind, with the use of the hands.
Free kicks under the first circumstance are easy to spot and are always paid, because a player already in the air cannot take a dive when pushed. However, under the other two circumstances, making judgement calls can be very difficult: it is easy for a player to take a dive in these circumstances; a sprinting player who is pushed may, in the act of trying to fall safely, take an unnatural leap which inadvertently makes the play look like a deliberate dive. As such, paying free kicks for pushes in the back in marking contests has always been contentious.
However, these pushes are all caused by the arms. Players in marking contests are allowed to push their opponents out of the contest with their bodies, within reason; so, a subtle nudge with the shoulder would not be penalised, but a full-blooded bump in the back would be penalised.
"Hands in the Back" 
In 2007, the AFL introduced an interpretation of the push in the back in marking contests, referred to as hands in the back. Under the rule, any player who placed his hands upon an opponent's back in a marking contest, whether there was a visible push or not, would be penalised.
The rule was introduced after a 2006 season, in which there was an increasing tendency for forwards to play from behind in standing one-on-one marking contests, using their hands or bodies to nudge their opponents under the ball. It has become very difficult to adjudicate whether or not these nudges should be penalised, and there was a high degree of inconsistency. The AFL introduced the hands in the back rule to remove the subjectivity of these calls: in other words, a push with the body/forearms/closed hand was fine, but a push with open hands was not, regardless of the strength of the push.
The rule has encountered a wide range of problems, with two particularly notable ones.
- Players were being penalised because they were unable to use their hands to protect their positions, or even feel the position of their opponent while their eyes were on the ball.
- Umpires were frequently caught in the wrong position to see hands in the back calls, so the application of the rule ended up just as inconsistent as the previous season.
There were repeated calls for the rule to be repealed, even midseason, and there has been much criticism of the AFL for introducing the rule into the regular season without trialling it first in the NAB Cup. The AFL has stated that the rule would remain beyond 2007, and fans' angst decreased as the season progressed, and as players became used to working within the interpretation.
The umpire signals a push in the back by holding both hands open, palms facing outwards, in front of his chest, then making a pushing motion outwards with them. However, his action often reflects the push which is being penalised: so, a push in a marking contest will see the umpire push his hands outwards, while driving a player into the ground will see the arms pushed further downwards.
Famous Push in the Back Incidents 
In Round 9, 2007, with the scores tied between Essendon and Richmond and with about three minutes to go, Matthew Richardson nudged Mal Michael out of a standing one-on-one marking contest, using his right hand on Michael's right shoulder blade. Michael, who was in front but slightly out of position, jumped to take the mark exactly as he was pushed, but missed the ball; Richardson took the mark and played on immediately, kicking the ball between the goal posts from 50m out, but was penalised for a push in the back, plus fifty metres for wasting time. The Tigers lost the game, and widespread debate about the hands in the back interpretation followed in the next week.