A 1/10 A30. A75 pulls to the right, leading the block on a sweep. While A75 is blocking B45 above the waist in the front, A44 (the fullback) blocks B45 from the front below the waist. A25, the ball carrier, is tackled at 50.

Give all options and clock status

My take:

Blocking below the waist/illegal block (Rule 2-3-7) by A44.
This is not a chop block as it did not occur within the free blocking zone.

B's option to decline and give A a first down on the 50 or take the penalty from the point of the foul (assuming it was behind the 50)and repeat 1st down. It's a 15 yarder. Clock starts on the ready.