AFL Umpires boss Jeff Gieschen has conceded the umpire made a mistake in penalising Crow Scott Thompson for a push out in a marking contest in the tense final quarter against Hawthorn at AAMI Stadium on Saturday.

With Adelaide leading by a solitary point, Thompson outmarked Hawks utility David Hale 30m out from goal with 15 minutes remaining in the game. However, the All Australian was adjudged to have given away a free kick in making minimal contact with Hale’s shoulder.

The Hawks then took the ball coast-to-coast and scored a goal to Liam Shiels, which put the visitors back in front.

“We’ve deemed it to be an error by the umpire,” Gieschen told AFL.com.au.

“The questions you have to ask are, was it a hand in the back? No, it wasn’t. There was a bit of a touch on the shoulder, but was it a push out? No, it wasn’t a push out either.

“To be a push out, there needs to be a degree of force, a straightening of the arm where there’s a visible push out. In this case, no it wasn’t a push in the back and it wasn’t a push out in a marking contest. There was a little bit of incidental contact on the shoulder, but certainly not a push out. It was a mistake by the umpire.

“Our coaches have spoken to Ray (Chamberlain) about that and he was comfortable with that as well.”

Coach Brenton Sanderson denied claims the decision cost Adelaide the game.

"I thought it should've been a mark. But the umpires were okay tonight, it's not the reason we lost the game," Sanderson said.

Gieschen offered an explanation for the ‘push out’ rule, which has generated debate following the Thompson incident.

“You can use your forearm as a bumer bar, just to put it up if players are coming back on you (in a marking contest), but you can’t extend it out to push someone out of the way,” he said.