godan verb (-mu), intransitive verb
Colloquial intransitive verb meaning to back off, retreat, or get out of the way. Often used in rough or informal speech, including commands like すっこんでろ (stay out of this).
うるさいから、ちょっとすっこんでてくれ。
You're being noisy, so back off for a bit.
あいつは怖くなってすっこんだ。
He got scared and backed down.