[AtlUmpSteve]

You have it right, Ted. Legally discarded equipment in fair territory becomes part of the field, and the ball touching it does not establish either fair or foul. Legally discarded equipment in foul territory does ground the ball, and the ball becomes foul by rule.

There is a one word difference in the definition of fair ball between ASA and NFHS. ASA definition says the ball is fair if it touches the "attached equipment" of a player over fair territory; NFHS definition doesn't include the word "attached". HOWEVER, the definition of a foul ball is clear, and definitively different, in that in NFHS it specifies any object foreign to the natural ground (while the ASA definition includes detached equipment.

Your clinician was apparently hanging his hat on "equipment"; but the ruling is based on attached equipment, not legally discarded equipment.