If a player from Team A is found wearing a bandana on the field, what will the umpire do?

When a player from Team A is found wearing a bandana on the field, the proper course of action for the umpire aligns with the established guidelines regarding unauthorized equipment or apparel. In this case, the umpire issues a team warning. This approach serves multiple purposes: it addresses the infraction without escalating the situation unnecessarily and allows the team a chance to rectify the issue. A warning also emphasizes compliance with the rules while preserving the integrity of the game.

In contrast, immediate ejection or requiring the player to leave the field would be disproportionate responses for a first-time infraction of this kind. These options could disrupt the flow of the game significantly and would typically only be warranted for more serious violations or repeated infractions. Similarly, opting for no penalty at all does not enforce the rules effectively, which is essential for maintaining fair play and safety standards on the field. Therefore, issuing a team warning is the correct and most appropriate action in this scenario.