unprovoked
adjective uk/ˌʌn.prəˈvəʊkt/ us/ˌʌn.prəˈvoʊkt/
(令人不快的言行)无端的,无缘无故的
If an unpleasant action or remark is unprovoked, it has not been caused by anything and is therefore unfair.
an unprovoked attack on her character 对她人格的无端攻击
Synonym: motiveless