WEST Coast coach Adam Simpson fears drastic measures such as reduced team sizes or creating bigger grounds could come into effect unless the AFL stops tinkering every year with the rules.

Teams will be capped to making 90 interchanges a game this season – down from 120 last year.

And the protected area around the mark has been increased from 5m to 10m this year after being trialled during the first two rounds of the pre-season.

Proponents of the new rules hope they will help encourage free-flowing football and reduce defensive congestion.

Simpson isn't quite sure where he stands on the new tweaks, saying it will take time to assess how they work. 

But he said it was important for players, coaches and fans to be able to have a consistent set of rules that didn't constantly change.

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"I just want to know why we're doing all of this. What's the reasoning?" Simpson said.

"To make the game quicker? To make it more fatigue-based? More one-on-one? More scores?

"It's hard to keep up sometimes.

"We've just got to be careful why we're changing things.

"Now it's this, let's just leave it at this. Let us deal with it, and work and strategise and expose, and do all the things coaches do with spare time."

Supporters of the reduced interchange cap hope the fewer rotations will lead to more one-on-one contests – a feature of the game that has dwindled over the past decade.

But Simpson said trying to "wind back the clock" was a dangerous ploy.

"We've just got to be careful that we're not trying to get back to 1990," Simpson said.

"Let's hope they don't get to the end of this year and go, 'We're going to make (the interchange cap) 60'.

"Or if you get subbed out, you can't come back on.

"You can't wind the clock back. The only way you can do that is you've got to get spots on the ground where you can't leave. 

"It's like the golf courses now have to be longer, because technology's too good.

"If you want more scoring and more fatigue, make the grounds bigger, or make the teams less, or don't touch it."

A glut of 50m penalties has already been paid during the pre-season for players encroaching on the 10m protected area. 

It's a rule change that Simpson isn't a fan of.

"I wasn't one of the 17 teams that was happily endorsing that rule. And now it's in," he said.

"But I'm not losing sleep over it." 

West Coast will play their final match of the pre-season on Sunday when they host Essendon at Domain Stadium.