Theoretical Chop Block?

[ajv]

A query came up in a recent meeting.

Defensive lineman B79 is blocked by A55 who is backing into pass protection. Three yards into the offensive backfield B79 throws off his blocker, turns and advances towards the quarterback. He is then blocked in the front by A34 at the thigh.

I read this as two separate blocks rather than a combination and therefore not a chop block.

What interval is necessary between clearing the high block before a low block is ok? Is the contact required to be simultaneous or near-simultaneous?

[SD_Casey]

I read that the same way you do.

A.R. 9-1-10-i says:

On a forward pass play, A75 is blocking B66 at the waist behind the neutral zone. While A75 maintains contact, A47 subsequently blocks B66 at his thigh. RULING: Chop block, 15 yards from the previous spot.

This leads me to believe that the first block must be maintained.  If B completely sheds A55 and they are no longer engaged when A34 goes low you have a legal block since the two were not made in combination.

The case for a chop block could probably be made if A55 were the one shedding the block though.  If he blocked B79 into or otherwise knocked B79 off balance into a position where he was then blocked low by A34 without maintaining contact.  In this scenario there's a possibility that the blocks were made in combination even though the initial contact was not maintained.