go in

verb6

1. •
   To begin or become involved in some activity.

   • I wish I'd known that going in.
2. •
   To become understood or accepted.

   • You have to tell him a hundred times if you want it to go in.
3. •
   To perform invasive surgery.

   • Our next step is to meet with Dr. Wells (surgeon) to discuss our next step. It looks like he will have to go in and see exactly what it is, then if cancer, extract it. — 2012
4. •
   To share in part of a project's or plan's duties or costs.

   • If you guys are fixing up that boat together to share it, I'll go in too.
5. •
   To become obscured by clouds.

   • It's chilly now the sun's gone in.
6. •
   (old-fashioned) To beat up or attack.

   • You went in on him with a knife?