You sit down and your dog settles at your feet. A passerby turns toward you, and the dog stiffens or growls. Whether they are worried about the person, the tight space, or someone coming near you, the safe response is the same: politely ask the person for distance and leave the bench calmly when you can. Do not ask them to offer a hand or treat to prove they are friendly.
Choose a quieter spot with room to move and keep your dog on a secure lead. Avoid tying them to the bench, a sudden lunge can injure them or someone else. If there has been a bite, repeated guarding of you, or difficulty controlling the dog, seek veterinary and qualified, reward-based behavior help. A new reaction deserves a health check.
Practice where escape is easy
On a wide path, reward your dog for noticing people at a distance and turning back to you. Move away while they are still relaxed. Later, pause briefly in an open area with no one approaching, reward calm observation, and leave. A bench can come back into the plan only when nearby movement no longer traps your dog into a reaction. Keep people from leaning over or reaching toward them.
You do not need to decide in the moment whether the dog is "protective." The growl says the current setup is too close. Giving room and avoiding a repeat are better than debating motive at the bench. If your dog guards the bench or space beside you, the resource-guarding guide may help you understand that pattern. Give passersby room and avoid testing it.
Sources: Dogs Trust: Resource guarding in dogs. VCA Animal Hospitals: Fears and Phobias in Dogs - Animals and People.