Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
The pig is a huge man with unlawful wealth, and he is a cursed enemy who does not keep a covenant. Riding one is gaining unlawful money and authority. Eating its meat indicates consuming unlawful money.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
The pig indicates a strong, unjust enemy. The domestic pig indicates fertility and prosperity that does not last. The wild boar indicates cold and rain.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
The pig is interpreted as a lowly man from the non-Muslims (Ahl al-Dhimma) or a conquering enemy. Whoever sees himself fighting a pig is fighting a strong enemy.