also: blind side block · blindside
A block on an opponent who cannot see it coming. What makes it illegal changes between high school, college and the NFL.
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A block delivered against an opponent from outside his field of vision, most often from the side or from behind. It commonly happens on kick returns, interception returns and plays where the ball changes direction.
A defender in pursuit is looking at the ball carrier, not at a blocker coming from the side. That leaves him unable to brace for the contact.
blind side blockcut block, crackback blockHigh-school, college and NFL rules do not define this foul the same way. Where the block happens, which direction the players are moving and how the blocker makes contact can all matter.
Teach players not to hunt someone who cannot see the hit coming, and check the rulebook for your level before teaching the details.
cut block