Tafsir of Ta-Ha 20:65

(They said): This is a connective (isti'naf) for an explanation, as if it were said: What did they do after they said that? Thus, it was said: They said: (O Moses). They did not mention their gathering and coming in ranks so as to signify the obviousness of their matter and that it is self-evident.

(Either you throw): That is, [either] you throw what you are throwing first, assuming the object is omitted due to its obviousness, or you perform the act of throwing first, assuming the verb is treated as intransitive.

(Or that you be the first to throw): [Meaning] what you throw, or the first to perform the act of throwing. They offered him the choice, peace be upon him, and prioritized him over themselves to demonstrate confidence in their own affair. It is also said: [It was] out of respect for him, peace be upon him.

"Ma" (what) along with what is in its scope is in the accusative case by an implied verb, meaning: "Either you choose your throwing, or you choose that we be the first to throw." Or it is in the nominative case as the predicate of an omitted subject, meaning: "The matter is either your throwing or our being the first to throw." Abu Hayyan preferred that it be a subject with an omitted predicate, meaning: "Your throwing is first," by virtue of the evidence of (or that we be the first to throw). With this, the contrast is completed, but it is [a contrast] in meaning.