(S (S (NP (QP (ADVP (IN At) (JJS least)) (NN 6,000)) (NNS protesters)) (VP (VP (VBD took) (BASENP (NN part))) (COMMA ,) (S (VP (VBN accompanied) (PP (IN by) (BASENP (NN riot) (NNS police))))))) (PERIOD .))