The protest turned into stone-throwing, leaving several officers injured.

stone-throwing 是由名词 stone（石头）和动名词 throwing（投掷）组成的复合名词，throwing 是动词 throw 的现在分词形式，表示"投掷"的动作。 stone-throwing 指"投掷石块"的行为，通常用于描述暴力抗议或冲突中向他人投掷石块的行为。