Anything that's protective safeguards or watches out for something (or someone) else. Protective gear keeps you safe from physical injury, and a protective parent cares for and worries about their children.
When you work with dangerous chemicals or toxic substances, it makes sense to wear protective masks or gloves, and a new bicycle rider is smart to wear a protective helmet. The first time you bring your new puppy to the dog park, you're likely to be protective of him, keeping him safe from bigger, older dogs. The Latin root of protective is protegere, "to cover in front, or to protect."