إِذَا أُحْصِرَ الْمُحْرِمُ بِعَدُوٍّ
Translation: When the person in ihram is prevented by an enemy.
Idha is a time adverb with conditional sense. Uhsira is passive past tense; al-muhrimu is the passive subject; bi-ʿaduwwin is a prepositional phrase.
فَإِنْ قَدَرَ عَلَى إِدْرَاكِ الْهَدْيِ، دُونَ الْحَجِّ: تَحَلَّلَ
Translation: If the offering is reachable but Hajj is not, he exits ihram.
In is the conditional particle and qadara the conditional verb; tahallala expresses the consequence.