What is a "crackback" block?

[Official_21]

Could someone tell me what a "crackback" block is and where it is covered in the rulebook?

Been trying to find it, but could not on my first read.

Thanks.

[TXMike]

Look for "blocking below the waist" 

Example of one:  http://www.youtube.com/watch?v=1lUB2rwrfKg

[Osric Pureheart]

When an official says "crackback", he almost certainly means a block below the waist towards the ball the wrong sideline.

However, I've come across a lot of coaches or players who use it to describe any block where the blocker starts wide and then blocks back towards where the ball came from, even if it's a high block, and I think it's worth being careful to not just say "crackback" and assume people are thinking of the same thing that you are.

[Official_21]

When an official says "crackback", he almost certainly means a block below the waist towards the ball the wrong sideline.

However, I've come across a lot of coaches or players who use it to describe any block where the blocker starts wide and then blocks back towards where the ball came from, even if it's a high block, and I think it's worth being careful to not just say "crackback" and assume people are thinking of the same thing that you are.

Yeah, I have seen the same description as above.

Thanks for the clarification all and if anyone has anything else to add please do so 

[Reverend30]

However, I've come across a lot of coaches or players who use it to describe any block where the blocker starts wide and then blocks back towards where the ball came from, even if it's a high block, and I think it's worth being careful to not just say "crackback" and assume people are thinking of the same thing that you are.

I think that's an important point to remember as well when a coach asks about the legality of a "cut" block - if it's not in the definitions, I think it's best to avoid it as terminology.

[beaye1]

As an old receiver, we were taught to make that block on the LB, DE or safety and make sure our head came across their chest or it was an illegal block(glad I don't have to worry about that now).  The one block that would give me the most pleasure was when the defender was coming towards me and I would hit him from the side "cracking his back" and sending him flipping sideways.  We called that a "crackback blocK" and it was never taught to be low.  Only block where we would go low was when we were blocking the DB and that only required us to block north/south and then hit the bround and roll but not necessarily make contact just to occupy him until the lineman came to provide that leagal low block.