This is mostly concerning the city center, can't really say anything about other parts of the town: Overall very safe, though there are some sketchy places in the city center where I prefer to not go alone after dark. Avoid the area around the mall at night as well as Stiftsplatz if there are no events happening. Any public gatherings with crowds are generally safe.

I know Kaiserslautern pretty well by know, and am generally a more anxious person but still am comfortable to walk around alone at night. In 8 years the only thing I have experienced is „only“ catcalling.

It's relatively safe. When there's a soccer match, the city is busy. During high-risk matches, fans are escorted separately through the city. On such days, the train station is closed. Since the Ramstein military base is nearby, many Americans are in Kaiserslautern. Therefore, the German police patrol jointly with the military police, which in itself isn't a bad thing. The city center is currently being renovated and is now much brighter in the dark.