A considerable part of their actions is very disruptive, seeking to, in the view of the protesters, I imagine, annoy everybody involved in the transport of nuclear waste to such an extent that they'll give up, while in actuality just causing a financial burden for the taxpayer (17000(!) policemen were in service during the protest you linked to according to [1]). That includes the traditional "Schottern" (the "[removal of] gravel from the bed of the train tracks to stop the train" as the article calls it), see also [2].
Even encouraging others to go "Schottern" on the internet is punishable[3] (sorry, again only in German) and punished, though.
And with respect to physical attacks, I think those protesters are rather harmless. I believe not a single policeman was injured in the aforementioned protests, even though thousands of protests were there (1500 at some point, 5000 at another point in time).
[1] http://www.zeit.de/politik/deutschland/2010-11/castor-gorleb... [2] https://de.wikipedia.org/wiki/Schottern [3] http://www.oberlandesgericht-celle.niedersachsen.de/portal/l...