"Your best player needs to rush in order to disrupt the QB’s timing, make him move from his starting point, and force the play in one direction."
An outstanding rusher can single-handedly remove as much as ½ of the QB’s field vision just by make him run towards the sideline. This is called “flushing the Quarterback,” and the best direction to “flush” the QB is away from his dominant hand. Make a right-handed QB run to his left and squeeze him between a relentless DL and the sideline. Any throw should be less accurate and less powerful, making it harder for the Offense to succeed.
In 5-Man flag football, any defense other than head-up Man Coverage opens you up to risk. The right zone can surprise your opposing QB and open the door for a defensive big play. The benefit is, if you guess right, you can counter their best plays or players. The problem is, if you guess wrong or telegraph your intentions, you can give up easy yards.
Zone in 5-Man flag is, to me, too big of a risk unless the opposing offense runs all its plays through one receiver. And you get this from time to time - one athlete who dominates and controls the whole game. In that case it may be worth the risk to try to neutralize their star with a zone.
Take the following play - Double Zone:
In versions of flag football where there are more defenders - 7-man and 8-man for sure fit this mode - you have enough bodies to cover a significant area in the secondary without abandoning pressure. But in 5-Man, it's almost impossible to cover the whole field with 4 players AND get pressure with the only rusher.
Also, in 6-man, 7-man, or 8-man flag, you can use zone to delay or slow down the Offense's momentum. But in 5-man, you just don't have enough defenders in coverage. Too often zone defenses in 5-man expose large chunks of open field for quick receivers to exploit. Zone allows Offenses to bunch receivers and create mismatches purely from formation.
Therefore, if you plan to use Zone in 5-Man Flag Football, I recommend it be
used as a surprise - a special defense designed to take away a specific player or a specific area of the field.
Remember, Zone is a risk, but it is sometimes worth the risk. If you put your best rusher at DL, you'll give yourself the best shot at success every time.