Tafsir of Al-A'raf 7:98

(Or do the people of the cities feel secure): This is a negation after a negation, intended for the sake of hyperbole in rebuke and severity. No sequential order is intended between the two, which is why the particle fa (then) was not used.

Nafi', Ibn Kathir, and Ibn 'Amir read "Aw" (Or) with a quiescent waw. It is used for one of two things, and the intent here is a disjunction between the punishment coming to them by night, and what is indicated by His Almighty's saying: (that Our might should come to them in the morning [ضحى]). This refers to the forenoon of the day, which originally signifies the rising of the sun or its illumination at the time of its ascent. It was then used for the time in which this occurs. It is one of the hours of the day according to them, which are: al-dhurur (the first glimmer), al-buzugh (the rising), al-duha (the forenoon), al-ghazala (the sun at its zenith), al-hajira (midday heat), al-zawal (the sun's decline), al-duluk (the sun's setting), al-'asr (the afternoon), al-asil (late afternoon), al-sunut, al-hudur (the descent), and al-ghurub (the sunset). Some name them: al-bukur, al-shuruq, al-ishraq, al-rad, al-duha, al-munu', al-hajira, al-asil, al-'asr, al-tifl, al-hudur, and al-ghurub.

As al-Shihab said, it is indeclinable if a specific day is not intended, and declinable if the forenoon of a specific day is intended, in which case it is in the accusative case due to being an adverb of time. It is a maqsur (shortened) noun, but if the ha is opened with a fatha, it becomes a madd (extended) noun. They have counted the term al-duha among those that are both masculine and feminine.

(While they are playing): That is, they are distracting themselves out of extreme heedlessness. This is a figurative metaphor (majaz mursal) for that, and it is possible that it is an isti'arah (borrowed metaphor), meaning they are preoccupied with that in which there is no benefit, as if they were playing.