There, Kingshaw has the opportunity to get his own back by pushing Hooper down the wall, but he doesn't dare because he is not as cruel as Hooper.

get 在这里是"获得、得到"的意思。 his 是代词 he 的所有格形式，表示"他的"。 own 在这里是形容词，表示"自己的"。 back 在这里是名词，表示"回报、报复"。 get his own back 是一个固定短语，意思是"报复、报仇"，指通过某种方式回敬对方之前对自己的伤害。