Briefly

Quoted from "The Huddle" -- http://www.the-huddle.org/issues/13/real-time-space-for-real-time-results/

Some parts are bolded for emphasis.

I may show the defense on a chalkboard. for some, it is very useful to move off of the chalkboard and onto the field. I like to place people on the field (or a shortened field) and walk the entire team through each position, and explain what the contribution of each position is to the team-D concept.

After fielding questions (taking special care not to get into a flurry "What if?" questions) we run the defense against a 70%-speed offense. After 5-10 minutes of reps, we go 100% live. This is the usual time for things to degenerate, or objectives lost due to competitiveness, so it's very important to ensure that the reps are not rushed, and are re-focused with the team defense concept in mind. This is also a great time for people to experiment at different positions to get a feel for where their strengths lie in this particular team D.

Wait.... you're supposed to introduce a concept and then reinforce it on the field? I kind of thought we just introduce it and then let them run wild.

Never would have guessed.