塞がる
ふさがる · fusagaru · JLPT N2 · verb-godan
to be shut up
塞 = plug or block; 塞がる = become plugged, meaning the thing itself is stopped up
The kanji 塞 means plug or block. がる makes the verb intransitive, so 塞がる describes something that gets blocked on its own. 塞ぐ is the transitive form, where someone blocks something.
塞 — roof 宀 + 共 (hands) over 土 + 土
Originally depicted hands stuffing material between bricks under a roof to block gaps, giving the core sense 'to stop up' or 'block.' From this came extended meanings like 'frontier pass' or 'stronghold' (a blocked, fortified place), read sài. The reading sè keeps the verbal sense 'to fill in, plug.'