فَعَقَرُوهَا (They hamstrung her): Does the plural form indicates that the whole tribe contributed in hamstringing her or the nine persons? or just one of them hamstrung her; who is Qadar Ibn Salef, as narrated in some texts, and everyone agreed on that?

The source of this Arabic word refers to hitting a camel’s leg to let it fall then to be slaughtered. Only an expert can do that, that is why Allah (swt) said:

 {فَنَادَوْا صَاحِبَهُمْ فَتَعَاطَىٰ فَعَقَرَ }

(But they called their companion, and he dared and hamstrung [her].) (Al-Qamar: 29)

فَدَمْدَمَ (brought down destruction): Allah (swt) shook the earth under them. Hence, Allah (swt) enforced destruction upon them so they were destroyed and became extinct.

بِذَنبِهِمْ (for their sin): Allah (swt) punished them because of their sin and what they have committed; they rejected their Prophet Saleh (pbuh). Allah (swt) is never unjust with His servants:

 {فَذُوقُوا الْعَذَابَ بِمَا كُنتُمْ تَكْسِبُونَ }

(“Then you had not any favor over us, so taste the punishment for what you used to earn.”) (Al-A’raaf: 39)

فَسَوَّاهَا (made it equal): He made the punishment descend upon them all equally; to all young and old.

Allah (swt) told us about the punishment of people of Thamud in other Surahs as well:

 {فَأَمَّا ثَمُودُ فَأُهْلِكُوا بِالطَّاغِيَةِ}

(So as for Thamud, they were destroyed by the overpowering [blast].) (Al-Haqqa: 5)

{ وَأَخَذَ الَّذِينَ ظَلَمُوا الصَّيْحَةُ فَأَصْبَحُوا فِي دِيَارِهِمْ جَاثِمِينَ % كَأَن لَّمْ يَغْنَوْا فِيهَا ۗ أَلَا إِنَّ ثَمُودَ كَفَرُوا رَبَّهُمْ ۗ أَلَا بُعْدًا لِّثَمُودَ }

(And the shriek seized those who had wronged, and they became within their homes [corpses] fallen prone % As if they had never prospered therein. Unquestionably, Thamud denied their Lord; then, away with Thamud.) (Hud: 68)

Once Allah (swt) names their punishment as overpowering and once a shriek or a shake.

 {فَأَخَذَتْهُمُ الرَّجْفَةُ فَأَصْبَحُوا فِي دَارِهِمْ جَاثِمِينَ }

(So the earthquake seized them, and they became within their home [corpses] fallen prone.) (Al-A’raaf: 78)

 {فَإِنْ أَعْرَضُوا فَقُلْ أَنذَرْتُكُمْ صَاعِقَةً مِّثْلَ صَاعِقَةِ عَادٍ وَثَمُودَ }

(But if they turn away, then say, “I have warned you of a thunderbolt like the thunderbolt [that struck] ‘Aad and Thamud.) (Fussilat: 13)

So it is all kinds of punishments; a thunderbolt, shriek, earthquake and overpowering that is why Allah (swt) in this verse described it as brought down destruction that killed every person in the state he was in, it is an overpowering punishment which stopped their hearts immediately and disabled their limbs, that is why Allah (swt) says:

  {فَأَصْبَحُوا فِي دَارِهِمْ جَاثِمِينَ }

(and they became within their home [corpses] fallen prone.) (Al-A’raaf: 78)