What must the umpire do when noticing a player in the coach's box not wearing a batting helmet?

When an umpire observes a player in the coach's box not wearing a batting helmet, the appropriate action is for the player to wear a helmet immediately. This requirement is rooted in safety regulations designed to protect players from potential head injuries, particularly from foul tips or other errant balls. Helmets are essential protective gear during play, even in the coach's box, as situations can arise where a player may be at risk.

The umpire's role is to enforce this rule promptly, ensuring that all players adhere to safety standards. Thus, the player must put on a batting helmet immediately upon notice of the violation to minimize any risk of injury.

Other choices do not align with safety protocols; for instance, immediate ejection would be an excessive response for a safety gear violation that can be corrected on the spot. Warnings to the coach may also be inappropriate as the immediate remedy lies in ensuring the player wears proper equipment rather than penalizing the coach. Allowing the player to continue without the helmet ignores the safety implications of the situation.