Bunch formations cause problems for defenses that are not prepared for them. When receivers reduce their splits in respect to one another it usually means that some time of pick or exchange route is about to occur. The split reduction is problematic for the defense for multiple reasons. First, you can't run press-man on both WR's. Alignment won't allow you to. Also, to run straight man against reduced splits is suicide. The offense will pick you off and open-up a WR to the inside or outside. Because of this threat, defenses have to stay in pure-zone or combo-man coverage.
The blitzology blog had a recent post to deal with these types of sets. The coverage techniques that are explained are excellent and identical to what I would do versus those particular sets. Especially the coverage that is explained about wide bunch. In 4-2-5 terminology we call this coverage "TRIO" and man the SS on the #2 WR and play blue coverage on the #1 and #3 WR's with the corner and free-safety.
However, versus tight-bunch formations this coverage adjustment is not as sound. The tight-bunch formation is displayed below:
This formation can be used to attack you with the pass just as easily as the run. The formation is very similar to a formation with a TE and two wing backs to the same side. So the first priority to defending this set is to align the defense in a way that prevents it from letting the ball get to outside. If you play normal "trio" coverage versus tight-bunch formations, you are not going to have a player in a position to force the ball inside. This concept is paramount versus this formation, because it is so easy for the offense to wall-off the interior players.
The adjustment of choice is "3-way". (This is a different use of the term 3-way then what I discussed in a previous post in respect to what Buddy Ryan called 3-way ). 3-way coverage seeks to allow for combo man principals to be in place, while at the same time establishing a force player to leverage the ball back inside. 3-way alignment looks like this.
This alignment puts the defense in a good position to play the run or the pass.
VERSUS THE RUN
Versus the run 3-way places the SS in a position to force the ball inside. The corner is assigned play-pass responsibility, and the FS is a flat-foot read player that plays the alley aggressively. The backer is cheated over to help on the outside running plays. The end also solidifies the integrity of the defense by forcing one of the bunch WR's to block him on an outside run. The defense has 4 immediate players to defend the run against the 3 WR's the offense has to block. The offense has to leave one player unblocked on any outside running play. (The other posibilities are option (not a big problem, because the SS is in position to play the pitch) and the chance that the OT can scoop the backer. If this happens coverage adjustments are the least of your worries.)
If the Z WR blocks out on the SS, then the offense is in a lose-lose situation. They have to decide which player they want to team-off on. Either the FS or backer is going to be cut loose.
VERSUS THE PASS
Against the pass the rules are easy. SS has the first man to the flat, if no attacks it, he sinks under the first WR outside. The Corner has the first deep route outside, he is going to pedal on the pass and read the WR's. The FS has the first man deep inside, his technique is essentially the same as the corners. If a deep receiver does not show in or out, then they play a "zone it" technique and help their partner. The diagrams that follow are examples of how the coverage will work versus various route combinations.
3-way coverages is simple to execute because it works off other coverage principals that are part of the 4-2-5 Defense. Other defenses can integrate this coverage into their schemes. The number one concern with implementing this coverage, is the ability of the force player (SS). This player needs to be strong enough to force the ball inside and agileenough to run with a wheel route.