THE EXTENDED protected zone introduced in the NAB Challenge is receiving cautious support from coaches as it opens up the game and encourages players to attack through the corridor.

The AFL has been trialling an increase in lateral width to 10 metres of protected area around the mark in the early rounds of the NAB Challenge and is expected to decide on whether it should be eight or 10 metres this week.

Western Bulldogs coach Luke Beveridge said the decision on the size of the zone depended more on "what looked right" after saying its introduction is a good move.

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Melbourne's coach-in-waiting Simon Goodwin described the new rule as a good innovation that was keeping the ball moving faster.

"They have done it for a reason and I think the game is starting to open up a bit," Goodwin said.

Football operations manager Mark Evans has been canvassing the opinions of coaches on the issue and hopes to have a decision in place as to how wide the extended area will be before each club plays its final NAB Challenge game.

Beveridge praised the performance of umpires in adjudicating the rule changes, but said the sling tackle remained a difficult decision for umpires.

He said he would prefer if the umpires did not pay free kicks for tackles that were borderline, but he had no issue with penalties being imposed for tackles that were "way over the top".

Melbourne skipper Nathan Jones said while cracking down on the dangerous tackle was justified, he thought it would be difficult for umpires to adjudicate.

"Whether they can predict whether there is any malice involved in it is a very tough call," Jones said.

Young Melbourne midfielder Clayton Oliver copped a fine for a dangerous tackle in his first NAB Challenge game and is receiving coaching to ensure he refines his technique so he doesn't fall foul of the umpires.