North Melbourne captain Andrew Swallow says he is not sure how he is expected to attack a disputed ball after controversially being penalised under the new prior opportunity interpretation.

Swallow was caught holding the ball against the Sydney Swans on Saturday night after winning the ball and then driving through an Adam Goodes tackle with his head down.

The AFL umpiring department recently introduced a stricter interpretation to discourage players from leading with their heads to win a free kick.

Umpires boss Wayne Campbell said the free kick against Swallow was because he didn't dispose of the ball, but Swallow he said he didn't know what his options were.

"I didn't think I had too much I could do there," the midfielder told SEN.

"'Goodesy' did a pretty good job in tackling, but unless they want me next time to do a squat and kick my head up, I'm not sure how else they want me to pick the football up.

"I don't think I've done a whole lot wrong. I've bent down, I've kept trying to turn, and 'Goodesy' kept turning with me … I was stuck in a pretty awkward situation."

Swallow was told by the controlling umpire that the free kick was paid against him because he "kept driving forward" after picking up the ball.

"So that means he probably wants me to back out of the tackle if that's what I'm supposed to do," Swallow said.

"I don't know what else they really want us to do in that situation.

"I thought it was a bit unfair, but we'll adjust as will the umpires."