Why is a 'crowbar circuit' referred to as a crowbar?

This name probably comes from engineers working on electrical installations such as railways. If it becomes apparent or suspected, that the line they are working on has become live, a quick and easy way to make it safe, is to throw a crowbar across the live terminals. This will cause an immediate short circuit, blowing a breaker or fuse. A large metal object such as a crowbar, would be to hand and ideal for making such a short circuit.

Crowbar protection is 'brute force' way of making a circuit safe. Instead of breaking a circuit, it deliberately causes an overload, in order to trip a safety device futher down the line.