There is no definitive answer to this question as it depends on the specific laws in your area. However, in general, 9 inch grinders are not considered to be legal for use in public spaces. This is because they are considered to be a potential safety hazard due to their size and power. Additionally, 9 inch grinders can produce a lot of noise, which can be disruptive to others in public spaces. If you are considering using a 9 inch grinder in a public space, it is best to check with your local laws to ensure that it is allowed.