A member of the AFL's laws of the game committee has conceded umpires made a mistake in handing a costly 50-metre penalty against Sydney captain Kieren Jack on Thursday night.

Hawthorn, who won a thriller by five points, scored a crucial goal after the siren at three-quarter time after Jack was controversially ruled to have entered the protected zone of Hawk Jonathan O'Rourke.

O'Rourke was brought within goal-scoring range with just five seconds left on the clock.

Under the so-called "east-west" rule introduced at the start of this season, opposition players are not allowed in a corridor five metres either side of the mark as well as a five-metre radius behind the player with the ball.