Roughshod means "brutal" or "without regard for the rules." If someone ignores established rules and regulations, they run roughshod over the law.
You'll nearly always find this word alongside "run" or "ride," as when a power-hungry politician rides roughshod over anyone who stands in the way of his success. We get this figurative term from the original meaning of roughshod, used to describe a horse whose metal shoes have sharp, protruding nails. This was done to prevent slipping, but during wartime it resulted in terrible damage to trampled soldiers. If you've been brutalized, you may feel someone's run roughshod over you.