Stevie Johnson made a clean, and legal block on Eric Berry last Sunday. It is unfortunate that Berry suffered a serious injury on the play. The league is trying it's best to protect players, but if they eliminate the 'cut block', they will fudamentally change the way the game is played.
The 'cut block' should not be confused with the 'chop block'.
A 'cut block' is a block made below the waist on another player. In order to be legal, the head and shoulders must be in front of the target. The hittee usually aims for the thigh area of his opponent.
A 'chop block' is when two players engage a defender simultaneously, one high, and one low. This is an ILLEGAL block. There is no place for it in the game.
The 'cut block' is usually executed by smaller players, like wide receivers trying to block safeties and corners in the open field. It is an equalizer that allows smaller players to compete with larger ones. Navy football is successful because of this tactic. They usually give away about 40 pounds per man, but can compete with the big boys by utilizing the 'cut block'.
At 160 lbs, if I took on defender up high, I could get knocked into next week. But by going low, I could get his attention and be an effective blocker in the run game. In fact, you could really get into a DB's head if they know you'r coming for their legs. They get so enraged with revenge at times, that it could give you an advantage running routes.
There have been many complaints that the Johnson'e block was illegal and that he should apologize to Berry. I'm sure he didn't intend to cause injury and that he feels badly for Berry. But it was a legal play.