أَوْ قَامَ أَبُوهُ.
Translation: Or his father stood up.
This is the second alternative in the book; the expanded sentence is «جَاءَ الَّذِي قَامَ أَبُوهُ».
جَاءَ: main verb; الَّذِي: relative subject.
قَامَ: verb inside the ṣilah.
أَبُوهُ: «أَبُو» is the nominative subject of «قَامَ», marked by wāw; «هُ» is the possessive ʿāʾid.
In the previous sentence «أَبُوهُ» was mubtadaʾ; here it is the agent of «قَامَ». The same «هُ» is the ʿāʾid.