Ad-Dukhan: (9) Nay, they are in...

(Nay, they are in doubt): This is an "abrogating refutation" (idrab ibtali) by which their certainty is nullified, due to them not acting in accordance with what it necessitates. The nunation (tanwin) in (doubt) is for magnification, meaning: in a great, immense doubt.

(They are playing): They do not say what they say—which is consistent with the negation of the matter—out of foundation and submission; rather, they say it mixed with mockery and play. This sentence is a predicate following a predicate for them. It is also permitted that it is the [primary] predicate, and the adverbial phrase is linked to the verb, having been placed beforehand for the sake of the [rhyme of the] verse-ending (fasila). The shift in person (iltifat) away from addressing them directly is due to the extremity of their stubbornness and their lack of receptivity.