Final answer:
The ruling for initiating contact with an opposing player whose helmet has come off is a personal foul, serving to protect players from head injuries.
Step-by-step explanation:
If a player initiates contact with an opposing player whose helmet has come completely off, the correct ruling according to most football league safety rules is b) It's a personal foul. This rule is in place to protect players from potential head injuries when they are most vulnerable. Engaging with someone without a helmet can lead to serious injury, so officials are tasked to enforce these safety standards by penalizing players who violate them.