How does a penalty corner start, and what happens if an attacker enters the circle early?

Under 2026 NFHS rules:

• Whistle start (Rule 10-2-1, since 2024): the official administering the corner blows the whistle to tell the inserter play may start. Either official may sound it. If the ball is inserted before the whistle, play is stopped and the corner is reset.
• Inserter position (since 2022): the inserter can't have both feet inside the field of play when the ball is inserted.
• Attacker in the circle early (Rule 10-3-3, changed for 2026): if an attacker enters the circle before the ball is played, the inserter must go beyond the center line. Before 2026, the offending player went back. The change makes the penalty clear and consistent.
• Delay: an inserter who delays putting the ball in play can get a green card. The corner isn't canceled; it continues once the card is dealt with.