Too many infielders?

[Four Seam]

ASA Tournament. Coach of 10U.
To my eye, the field seems to have an abnormally large distance from home skinned. I have my outfielders playing on edge of grass for first several batters, then when a small batter comes up, I call to my outfielders to move in two steps, which puts them on the gravel. Blue calls time and tells me that's too many infielders, my outfielders have to be on the grass.

Is this correct? I can't remember the word "grass" appearing anywhere in the ASA rulebook. I have coached high school games played entirely on dirt. Also, I read Rule 6 (Fast Pitch) Section 5A to say that all defensive players except the catcher must be in fair territory, nothing more.