I read the USA Today article that Doug linked today, which amounted to an interpretation of a Peter King tweet. Only KSK should be interpreting PK, because this reporter follows him down the path of wrong.
They mention "legal chop blocks," but there are no such things in the NFL, nor have there been any in quite a few years. The problem is apparently confusion about what "chop block" means.
Allow me to explain.
A chop block is when a blocker is engaged with a defender up high, and a second offensive player goes low on the same defender. There must be two blockers on one defender, and one must go high, and the other low, for it to be a chop block. That's a 15-yard penalty on the offense.
I suspect what these guys mean by "legal chop block" is a cut block. The cut block is a legal play in which the blocker aims for a defender's thigh, in order to get him on the ground. Every team does it, but it's most common in zone schemes, where the backside blockers are trying to open up cutback lanes for running backs. (Broncos fans are well-steeped in this.)
Another important application for cut blocking is the short passing game, particularly screens and the three-step game. When you cut a defensive lineman in pass protection, he drops his hands to protect himself, which opens up throwing lanes from the QB's shallow set.
On a screen, linemen are usually out in space on LBs and DBs, and cutting them is tactically superior to trying to dance with them, unless you're Ryan Clady.
There's nothing wrong with a correctly executed cut block, regardless of what defensive guys will tell you. They don't like getting blocked, and they bellyache about successful tactics.
Now, there is a fine line, and blocks below or at the knees are dangerous. I do think the NFL should consider penalizing excessively low cut blocks, with a goal of getting blockers to raise their target area above the knees. That's no more egregious than asking a defender to aim shoulders-down on a defenseless player.
The NFL is emphasizing safety, for a mixture of some genuine concern for players, and (more serious) concern for financial liability. I'm not surprised that low blocks will be reviewed in the offseason, or that they chose PK to commit a daily act of lapdoggery.
However, I would be very surprised if the cut block is ever totally outlawed. With more and more colleges using it, it will get harder and harder to find blockers who are ready to only block up high. It's also an important tactic in today's NFL, and it causes fewer injuries than the media would have you believe. I can't imagine the football people on the competition committee would allow it to be banned.