49ers LT Joe Staley revealed that C Eric Heitmann suffered his career-threatening neck injury in former coach Mike Singletary's infamous "nutcracker" drill.
Singletary was the only coach still using the drill, which was more common half a century ago. The nutcracker involves two like-sized players crashing into each other to gain leverage. Patrick Willis (ankle), Tarell Brown (toe), and David Baas (broken foot) also sustained injuries from the drill. Upon installing the nutcracker, Singletary labeled it "pretty foolproof." The players felt differently.