Actually, zone blocking is very effective when O-lines are facing defenses stacked at the first level or overloaded sides. Zone blocking is just what it states it is--> Zone blocking. To simplify..... Linemen will take steps in certain directions based on playcall. As Bob Davie stated in his article, the line must all work togethor. If one lineman fails to move into the correct direction or in his "zone", slanting/stunting D-lineman or blitzing LBers can cause destruction. The most difficult aspect of Zone Blocking, IMO, is the combo block. As Bob Davie stated above, it appears to be a doubleteam, but the paired offensive lineman MUST keep their eyes on the LB on their side of the Zone at all times. One of them will "scrape" off and catch the LB. The problem is they must know who is going to do this at the exact moment. To help understand this, it's very similar to QB's reading defenses. It takes alot of pratcice and teamwork to get this rythm down. Of course, if your lineman are getting killed at the point of attack (not getting a push at the LOS) you're gong to lose teh battle up front no matter what style of blocking you run.