I came across this video and found it interesting. In the video that was used as a guideline for all players, the NFL explains the difference in what is not legal and Illegal. A wide range of topics were covered, including but not limited too... horse collar tackles, inadvertent contact with a QBs helmet, defenseless player contact, what is a catch, what is not a catch, what defines a defenseless player ect. ect.
It is an interesting video and gives us an idea of how the rule changes were presented to the players. If someone else has posted this prior to this, I apologize. This is the first I have seen of it.
Post note: the narrator sounds like he is talking to a bunch of 5 year olds. I know NFL players are not always the brightest candles but damn.