The junk will only trap when the disc is on the sideline. The disc can be on the sideline in two scenarios- the first being when we throw it in off the pull and it rolls out of bounds. The second being when we throw the disc out of bounds (when on offense) and the opposing team has to take it on the sideline. In this situation it is off the pull.
When the disc is on the sideline we will be trapping. The junk should be doing this automatically but Josh and I will be yelling it as well. In a trap the mark or in this case "1" will force sideline and the poach nearest to the sideline, in this case "2" will keep their inside foot on the sideline and extend the mark into the out of bounds space to force a throw further out of bounds laterally. The number "2" poach in this case is on the LEFT sideline so their RIGHT foot should be ON the sideline. The one big difference in this trap is the poach away from the other sideline, in this case #3. In a trap, #3 takes away the swing pass to the middle instead of poaching the lane (because the mark is forcing a specific way).
If the player who is in the middle (ready for the middle swing) realizes they are being covered (in this case "2" on red) and drops directly behind the disc for a reset, the poach away from the sideline ("3") goes back to their original poach position and allows that pass BACKWARDS. Remember, as a junk defense our emphasis is for them to pass it laterally and especially backwards so let's let them
When the disc is moved off the sideline (even a little bit) the junk follows its regular form because the huck option is now open along the sideline.