A combination or combo block is one in which two offensive players initially engage a defender to block before one of the offensive players disengages and engages a second, designated defender.
Usually you have two offensive linemen engaging a defensive lineman and then one of the linemen goes to block a linebacker. Which lineman goes for the linebacker is dependent on how effective the initial block is. The defender will usually end up more in front of one offensive player than the other. It is the other offensive player, who will go block the linebacker.
The diagram above assumes that the blocker on the left will be able to push the defender to a point in front of the blocker on the right before going to block the linebacker.
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