The Patriots have been trying to implement an offensive scheme known as a "zone-scheme". The zone-scheme is a blocking scheme designed to counter the defensive line "slant" schemes that starting being used in order to free-up Linebackers to attack through gaps created at the line of scrimmage.
For many years defensive coordinators were running line stunts and slants instead of just rushing up the field and attacking straight ahead into the offensive backfield.
These stunts and slants would force offensive lineman to move laterally in the same directions.
Run plays often call for a couple of the offensive lineman to help block the same defensive lineman for a second or two and then head up-field to engage Linebackers or Safety's.
By slanting the rush of the defensive linemen it would force an O-lineman to move laterally and chase his initial blocking assignment. Once the O-lineman reached his initial assigned block on a D-lineman he would then have further to go in order to get back to the second level to where his 2nd blocking assignment would be on a Linebacker or Safety. Usually the path to get out to the Linebackers was clogged-up due to the other slanting D-linemen and the chasing O-lineman.
This slant rush of the D-line would also create gaps for the Linebackers to penetrate thru or for to fill rush lanes without having to fight thru big O-linemen.
What caused big issues with the man-blocking scheme was the 3-4 defense and zone blitzes. The 3-4 defensive scheme would rush with the three down lineman and one of the other Linebackers, creating a typical 4-man rush.
When facing a 3-4 defense it was hard for the offensive linemen to know who they were assigned to block before the snap because they were never sure which of the Linebackers were going to be rushing, and from what side they would send the Linebacker from.
This created match-ups in favor of the defense. There may be an Offensive Tackle who ended-up not really blocking anybody because that Outside Linebacker dropped back into coverage or just didn't rush up the field. That forces the Offensive Tackle to take that extra second in order to find a rusher in his area to block. That extra second is all a defense needs to overwhelm a certain attack point which is lacking a blocker due to this delay in figuring-out which defenders were rushing and which defenders weren't.
On run plays you may have an O-lineman looking at what seems to be his blocking assignment before the ball is snapped. Once the ball is snapped that O-lineman would head in the direction of what he perceives to be his assignment, only to have that D-lineman, Safety or Linebacker drop off the line of scrimmage once the ball is snapped.
That is the problem with the man-blocking scheme. The O-lineman is assigned to a match-up and is expected to block that man, wherever he goes. Often he would end=up running himself out of the play.
With the zone-blocking scheme, the O-linemen are assigned a target in front of them. These blocks are initially double-team blocks by the Guards and Tackles. After the initial double-team block, either the Guard or the Tackle will then proceed to an area or a "zone" and block whatever player is there. Thus, they are never chasing assigned defenders.
The secondary blocks are expected to be on Linebackers and Safety's, preventing them from getting to the play side and making tackles. If there is no Linebacker or Safety in the zone in which these secondary blocks are expected to be carried out, the lineman will proceed downfield on the play side looking for defenders to block who are in the zones where the play is designed to go. The lineman are never seeking-out a particular player that was per-determined before the ball was snapped.
This prevents lineman from chasing defenders out of the play side attacking area and rendering themselves useless and unavailable to make blocks in the attacking zone areas.
This zone concept makes Linebackers and Safety's vulnerable to blocks if they are at the point of attack no matter where they line-up. If they are in the attacking zone, or run to it, they can expect a blocker from somewhere to be heading into that area as well.
Running backs that are running behind a zone blocking scheme will usually get the hand-off and and advance with some hesitation while they're looking for gaps in the front as the D-lineman are being pushed one way by the double-team blocks.
Once that gap is recognized he will head for that gap and towards the second level defenders, who will hopefully have a block heading towards them by an O-lineman after he releases from his initial double-team block, or "chip" block, and heads to the 2nd-level defenders, as well.
The zone-scheme concept is generally and easier ask for the offensive linemen. They just need to head to their designed target areas and block whoever is there, instead of pre-determining a defender to block, recognizing where he is heading after the snap, and then getting to him in a blocking position wherever he may go, as needed in a man-blocking scheme.
The thing with the zone scheme is that the O-linemen need to be agile and athletic enough to move from their initial double-team blocks to their second-level assignments. This tends to require smaller and more agile linemen, as opposed to the bigger, stronger in-line blockers needed in a "man" or "gap" blocking scheme.
They are also asked to "pull" and run to the play side from the other side of the Center, which is shown in this picture below.
Since the zone-blocking scheme became very effective, defenses have had to figure-out a way to attack it.
One technique used is a gap penetration technique.
The object of this is to have the D-linemen line-up in the gaps between the O-linemen. They will then quickly shoot into those gaps when the ball is snapped, thus preventing them from getting washed-down by the double-team blocks in a direction the blocking scheme is designed for them to be pushed.
This technique will also cause the running back to make a quicker decision and have reduced ability to quickly find a gap in which to run thru.
Another technique used is the "wall" technique.
The D-linemen will latch onto the lineman directly in front of him and try to prevent him from getting off the initial block and continuing to his 2nd-level block.
In so doing, the D-linemen will try to create a wall of bodies at the line of scrimmage and keep the Linebackers free to seek the ball carrier and/or the gaps he may be looking to run thru. This is probably why it seems we see many more holding calls on defensive linemen recently.
Hopefully this gives you a better understanding of the concept when you here announcers talk about a teams zone-blocking scheme, which the Patriots are in the process of implementing.