Below is the link to a training video from the Arizona Football Association. Comments from the OHSAA staff:
The second chop block example is suspect. From this angle the high contact does not appear to be a block. If the contact is seen as a block it is a foul, but otherwise it would be okay to pass on it.
The block by the B defensive end is also suspect. It doesn't appear that he initiates the block and the A player simply falls on top of him. Suggest we pass on that one.