Tafsir of Al-Anbiya' 21:12

(When they sensed Our might...)

The plural pronoun refers to the people [of the city], not to some other folk, for the latter would have had no sin.

What this discourse entails is that "sensing" (al-ihsas) means perception by way of a sense; that is: "When they perceived Our severe punishment with their senses." Perhaps that punishment was of a nature to be perceived by one of the outward senses. It is also permissible that "might" (ba’s) involves a metaphorical metonymy (isti'arah makniyyah), with "sensing" being a form of imaginative representation (takhayyul), or that "sensing" is a figurative expression for absolute perception—meaning: "When they perceived it."

(Behold, they from it...)

That is, from the city, in which case "from" (min) indicates the point of origin; or [it refers to] "the might," and the feminine pronoun [used for "it"] is due to it bearing the meaning of niqma (vengeance) or ba’sa (adversity), in which case "from" is causal. Under both possibilities, it relates to His saying, the Exalted: (are fleeing/rushing).

("Ifa" is for suddenness, and the clause is the response to "When" (lamma).)

Rakada is from the category of qatala (nasal-a), meaning to strike the mount with one's foot. It is transitive, though it may also appear as intransitive, as in "the horse ran" (rakada al-faras), as Abu Zayd stated, and those who denied this carry no weight. "Rushing" (al-rakd) here is a metonymy for fleeing; that is: "Behold, they are fleeing, hastening and spurring on their mounts." It is also permissible that the meaning is "resembling those who spur on mounts," based on there being a dependent metaphor (isti'arah taba’iyyah). There is no barrier to interpreting the words literally, as has been said.