Today at the airport I saw a Delta MD-80 land.  He touched down lightly and put down the front wheel.  However when he engaged the thrust reversers the nose of the plane pitched up to about 15 degrees and were quickly disengaged and the elevators went full down and the nose hit the ground hard.  What do you think happened?

Aircraft with tail mounted engines do have a tendency to pitch up in reverse, due to the location of the engines.  It sounds like this pilot either engaged reverse too quickly, or was not ready for it.  When I got some time in a MD-11 sim, you had to hold the nose down with the yoke when engaging reverse.