porterste

Help please. My escort cosworth engine was rebuilt about 18 months ago a few weeks ago I was driving it hard and something seemed to grab luckily I dipped the clutch quick and turned off. The temp was showing just below the red. On trying to restart the engine it was turning over slow but would not start. I got a mate to pick me up with a trailer. the following day it started fine and seemed to run OK but the oil pressure was low. I decidedto take the engine out and strip it and found that the back main bearing and No 4 big end were down to the copper and the crank was a mess. I have took it to the local machine shop and they have said the block was twisted. How has this happened?