The disc is trapped on the sideline, we're playing zone defense. The offense is looking to swing... We are red and the offense is blue.
Often, more experienced teams will attempt to swing it all the way across the field. This is where our wing, #7, needs to be aggresive and get there with the D. It's ok if they leave #2 (blue) open because the thrower will either have to throw a hammer or a blade to get it to them - both of which are difficult and give #4, our deep a play on the disc. They should start their play by first recognizing what is happening when the disc is caught by someone on the sideline, and then closing the distance between them and the handler in anticipation.
Boom, he D'd it because the handler was looking at the disc and not at him. This is an easy way to get turns against experienced handlers who (hopefully) won't expect this play.