to (enter and) sit down; to plop oneself down; to plant oneself down
to sit down (and refuse to move); to sit in (in protest)
疲れてその場に座り込んだ。
I was tired and sat down right there.
抗議者が入口に座り込んでいる。
Protesters are sitting down at the entrance.
長距離を歩くと疲れて座り込む場合がある。
When you walk long distances, you may get tired and sit down.