There are a few more things to cover as basics before going on with the full schemes, which I can hopefully get to before the season begins.
Play-action passing gives rise to another technique to be used in certain situations called a Double Read. Its not a very common thing to try, but the use of the spread and having to block with only 5 makes it a little more important for those types of offenses.
A double read is a technique used by a lineman who is covered by a LB at normal depth, with an opposing DL on the OL adjacent to him. The first step of the technique is simply a Hard Post to the inside. While he's using his inside arm on the DL, helping his teammate, his eyes should be on the feet of the LB over him. If the LB does not blitz, he carries on with the regular hard post maneuvering. But, when the LB does blitz, he disengages from the DL and sets himself square to block the LB by pushing hard off his inside foot and shoving the DL inside to his teammate. His teammate now has the DL one-on-one.
This type of thing is common on the backside of a protection or against some 4-3 fronts. Since play-passes are off a run fake, the backside protection can get outnumbered and occasionally flanked by some structures. Often the RB goes strongside, and they don't have help if the defense blitzes into the backside of the play-action. You would rather not have him fake strong and then cut back to the weakside, because that could clue the LBs that this is not actually a run play and is instead a pass. If you can't outnumber the defense and get blitzed backside, the simplest way to pick it up is by using the double reads.
But its not foolproof by any means. Two or three OL still can't be counted on to block 4 if the defense runs a Fire Zone call, or other weakside blitz with 2 linebackers. You can cause problems for a double read by blitzing both backside LBs when flow goes away, but this can also put the defense in a bind in coverage. Its a definite risk.
Against some 4-3 fronts, its possible to have two OL performing double reads: the Center and a Tackle. For example, if the defense aligned in an EVEN or a G-front (two 2-techniques, or a 3 + 2), the Center is not covered by a NG. A MLB is usually at 5 yards depth ahead of him. The tackle would have a 5/6-technique defender in most, but if theres a TE the DE sometimes slides out further, leaving the tackle uncovered. In such a case, both would start out by helping the lineman to one side, but if the defense blitzes a LB or SS, someone has the responsibility of picking him up. Hopefully the Tackle can get back there against an OLB blitzing off the corner.
When a LB aligns with two DTs to form a triangle over the A-gap, e.g., a 3 tech, a NG, and a MLB or WLB, the guard must be able to recognize and alert the OT that a triangle exists. Where the NG is aligned is not always easy for the OT to recognize so that he may diagnose the defensive front structure and know whom to pick up.
Whenever the OG is aligned on a 3-technique, he must let the OT know where the 1-technique defender is aligned, assuming there is one. With a defensive triangle like this there is a good chance of a stunt coming from the defense, or a blitz up the A from the LB. This procedure is meant to be an adjustment so everyone knows their responsibility, especially for man-to-man pass blocking.
The guard is looking for the LB to flatten the triangle (walk up to blitz), in which case he must alert the OT "backer inside". Should the LB blitz, he will be the guard's responsibility, and the OT must jump over to pick up the 3. A H/TE or RB has to block/cut the DE in this case. If the LB backs off, the guard and tackle can either stack the 3 (two-man block) or go one-on-one with the 3 and DE respectively.
Even if the scheme for that play does not call for a triangle read, the linemen should use the same alert calls always. If the 1-tech is inside the OG, he must always alert the OT. If the backer walks up, he must always alert the OT. If he doesn't, the defense will pick up the play calls.
There is also the chance of a stunt from the triangle, which will usually be with the 3-tech going inside to the A, and the LB twisting around to the B-gap. If the OG and OT are on the same page after the alert call, the OT will know to start blocking down on the 3. He'll see the 3 trying to cut inside on the OG, and start looking for a stunt from the LB, who is then his responsibility.
Since all the basics have been touched on, we'll go back and hit on some overall schemes for some plays for both the run and the pass in the next few posts before the season starts.