But what do the data measure?
"...defined here (following the violence-prevention organization Over Zero) as physical harm or intimidation that affects who benefits from or can participate fully in political, economic, or sociocultural life."
"Intimidation" covers a lot of ground. Based on some of the incidents mentioned in the essay, it would include all of the threats, doxxing, etc going on. For example, every individual such act against a LEO, for which neither "left" nor "right" currently has a good track record. Also, if "one riot" and "one threat" each count as "one incident", it's obvious the data aren't much use.
More use would be counts of actual shootings, bombings, riots, etc. What would be a lot? Apparently the FLQ alone did over 200 bombings (presumably all in Canada) during its run in the 1960s, and I've read claims that the US was averaging 5 a day at the height of domestic unrest in the late '60s and early '70s.