NY Giant fumbele on handoff caused by back, not QB Manning

There was a basic error in Monday Night Football tonight by the Giants, reminiscent of the four fumbled center-QB exchange in Saturday’s Army-Navy Game. The announcers semeed to blame Eli Manning. It was the running back’s fault, not Manning.
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I just looked this up in my football books to point out what page it’s on. I could not find it! I can’t believe that. Every running back I ever coached will surely tell you I taught it to them a million times.
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To receive a handoff, the running back focuses his eyes on the hole he is running to, not the ball. He puts the arm closest to the QB up, forearm parallel to the ground, and the arm farthest away from the quarterback down, also with the forearm parallel to the ground. When he feels the ball against his belly button, he clamps down on it.
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Here is the key point, which I could NOT find in my books! The pocket the running back makes must be big enough to receive a BEACH BALL. What the running back must NOT do is make a pocket that I call a “MAIL SLOT.” In old buildings, the mailman often puts the mail through a small slot about 7 inches wide by 2 inches high.
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The Giants running back made a mail-slot pocket. Mail-slot pockets cause fumbles. The mail slot pocket the Giant running back formed caused the fumble.
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What is the principle here? The pocket cannot be too big, but it CAN be too small. By thinking beach ball, the running back probably makes it bigger than the football, but bigger than the football is not a problem. SMALLER than the football is fumble city.