Definition
Deep is the back position in a zone — typically a single player, positioned far enough downfield to genuinely threaten any over-the-top shot. The deep is responsible for the entire deep lane behind the front and middle layers and for communicating downfield threats back to the rest of the zone.
In Context
A good deep makes the deep shot uncatchable — not by intercepting every throw, but by sitting in a position where the thrower cannot see a clean window. The deep's positioning bias depends on the wind, the matchup, and where the disc is on the field. Into the wind, deeps can sit deeper because the disc will not travel as far; with the wind, they need to be deeper still because hucks travel further than expected.
The deep is also the eyes of the zone. Front and middle defenders are facing the disc — they cannot see downfield threats developing behind them. The deep's job is to call out cutters who have broken into deep space and to position the wings off swings before the throw happens.
A deep who chases the disc forward into the middle layer is one of the most common ways a zone gets scored on — the deep lane is now open and the offence does not need to throw a perfect huck to use it. Hold the deep position.