The AFL umpiring department has admitted Callum Mills should have been called to play on in an incident that cost Adelaide a goal in the final quarter of the Sydney Swans' thrilling three-point win on Friday night.

But, they are standing by their call not to penalise Lance Franklin for "probably" running too far in what will go down as one of the goals of the season.

In the first incident, Mills took a mark on the Swans' defensive 50 and instantly took a step as he looked to handball. 

He was expertly tackled by Adelaide's Eddie Betts, but instead of winning a free kick, Betts was slugged with a 50m penalty because the umpire did not call play on.

"What we would have liked in that situation would be the umpire quickly call play on," head AFL umpires coach Hayden Kennedy said on Monday.

"What we saw was Mills control the ball, and in our belief, he then made an effort to play on.

"The expectation is from us is when Callum did go forward on the mark and go through the play-on motion, our expectation as a group is to call play on."

"That would have been the best result for us."

At the time, the Swans were trailing by nine points and there were just over six minutes left in the game.

The 50m penalty against Betts saw Sam Reid mark and goal, which narrowed the margin to within a goal. 

The match-winner came two minutes later when Tom Papley goaled and sealed the Swans' victory.

Meanwhile, Kennedy conceded Franklin likely ran almost 20m without taking a bounce – well past the allowed 15m – in his incredible third-quarter goal where he ran down the wing from half-back.

But, he acknowledged it was almost impossible to judge Franklin in that instance, as he was a "really fast man with long strides".

"I'm sure if the umpire felt he ran over the 15m, he would have paid it," Kennedy said.

"We paid two on the night, which I haven't seen for a long period of time, but it was a very marginal call as to whether or not he ran over the 15. 

"I think if you go slo-mo, I think he's probably closer to the 20 than 15. That's a fact, but live, I think it would be really hard for the umpire to tell if he's run over the 15.

"It still could be [goal of the year], because we didn't pay a free kick."