Did this happen during a tool change (e.g. the carousel was supposed to be in, and the head was supposed to come down, but the head came down too far)?
If so, you may have a parameter-setting error: somewhere there is probably a parameter that sets the Z position for tool changers. If it gets corrupted (set to a larger negative value) then the head would come down too far.
Or did it happen during normal run (e.g. the carousel was supposed to remain out, but moved in and got in the way of the head)?
If so, you may have a wiring fault or PLC output fault that allowed power to the carousel slide when it was not commanded to do that.
Did anyone see the crash? What was the machine supposed to be doing at the time?