AFAIK, no one was hurt. And the union status of the taxi drivers involved got little to do with the case, pretty sure all taxi drivers, unionized or not, feel the same about people that chose to do the same work as they do, without respecting the same rules as they are.
Violence is "the intentional use of physical force or power, threatened or actual, against oneself, another person, or against a group or community, which either results in or has a high likelihood of resulting in injury, death, psychological harm, maldevelopment, or deprivation.
For example, kidnapping the boss to prevent layoffs (or at least get better severances) is something that happens regularly.