When you think about workplace violence most people think of employees hurting other employees. This is not always the case. Workplace violence can have many causes and many perpetrators.
If you have delivery people, they may be robbed or harassed. Customers may cause problems as well. If you work in an industry that has a focus on customer service there is little doubt you have run into problem customers. Your motto may be the “customer is always right”, but when that customer is abusive or violent then they cease becoming a customer and instead become a threat to your employees and business. Other problems occur when employees family and domestic matters get dragged into the workplace. These are especially hard because you want to protect the individual employee but at the same time you need to protect your other employees and assets.

Here is a good resource about workplace violence. It is run by Barry Nixon an expert in workplace violence issues.