Glossary
Pinch
In one line: Attacking a site from two directions at once, so the defenders cannot watch both.
What it means
A pinch is a two-sided attack: part of the team enters through one entrance, the rest through another, at the same time. The defenders are caught in the middle and have to choose where to look.
It is similar to a split, but the idea is specifically to squeeze defenders from opposite sides. It works if both groups arrive at the same moment: if one arrives first, the defense deals with it and then turns to the other.
An example
On a site with one entrance from main and one from mid, two of you come from mid and three from main in the same second. The defender watching main gets shot in the back by the players coming from mid.