yeah, intention is too tricky.
in order for a threat to be credible, the periodic (and often arbitrary) use of force leading to physical or emotional harm is necessary. the intention (to frighten) is beside the point -- it is the exercise of controlling power that is the key to understanding what "violence" is.
a better question for anarchists might be "what do anarchists understand as legitimate violence?" plenty of anarchists throughout the last 180 years have discussed the a priori legitimacy of self-defense, the use of physical force to prevent someone from harming you. then there's the question that dot raises, which is the inherent violence present within systems; anarchists have argued that capitalism, with its reliance on the state to enforce particular property relations, is inherently violent (threats of jail and starvation being high on the list of objectionable and violent acts for non-compliance), as are the day to day mechanisms of government. the extension of this argument into the realm of anarchist action is that any attack against capital and/or the state is legitimate self-defense.