THE AFL has acknowledged a free kick should have been paid to Brisbane Lions defender James Polkinghorne for his tackle on Fremantle's Stephen Hill during the final quarter of Saturday night's game at the Gabba.

At the time Polkinghorne laid the lunging tackle, the Lions were leading by 10 points with less than four minutes remaining.

While it appeared Hill had failed in his attempt to kick the ball, play was allowed to continue. The Sherrin ended up Dockers forward Nat Fyfe, who kicked an easy goal to cut the home side's buffer to just four points.

Fremantle then snatched an improbable two-point victory when Michael Walters slotted a banana-kick from the boundary.

AFL umpires' manager Jeff Gieschen spoke about the decision involving Hill on OPSM What's Your Decision?

"At the time he was tackled, he went to kick the ball but unfortunately, instead of kicking the ball, the ball came off his knee, which is deemed to be an illegal kick," Gieschen explained.

"Our umpire, who was running with the play and watching, believed the ball had actually come off his shin, which would've constituted a legal kick.

"Unfortunately, when we freeze-frame the vision we can see the ball contacting the knee and then propelling forward, which means that this is an illegal kick.

"Therefore, the decision is incorrect. It should've been a prior-opportunity free kick to Polkinghorne for holding the ball against Hill."