Every and I mean every practice drill has some element of potential injury, all of them! Like anything else, there come great reward at great risk. Because of the nature of the drill where both men seriously man-handle each other, legs and feet can cross, players thrown to the ground, bruising, soreness, and the possible tweaks or worse yet, breaks.
They all happen in different degrees on different drills. The Nutcracker does toughen up the players and make them hone in on technique. Sure, Baas got injured and I think so did P-Willy, but most came out unscathed.
From what I have seen personally, The Nutcracker helps with stamina and direct one-on-one blocking techniques. Not only that, it makes us fierce and violent!
Those two attributes are now synonymous with Mike Singletary's team and his drill.