Much has been made of the astounding number of drive killing Chop-Blocks (or Crack-Back-Blocks depending on which part of Subjectivia you are from) the Cowboys have been flagged for this season, and even more has been made of Coach Gundy's comment when asked about it:

I told the team after the game that I am really unsure, myself, of what [the chop block] rule is and we will identify what the problem is and we’ll get it cleaned up.

Well I am here to help. Behold the graphic that depicts exactly where you can hit someone, and under what situation it is alright or not alright to do so.  It is just so clear cut!