It is a good idea to stay out of the way of anyone “hell bent for leather.”
The word bent has meant a mental inclination other than straight since 1586 and resurfaced as “bent out of shape,” meaning “extremely upset or weird,” during the 1960s.
“Hell bent” means the disturbed subject is in a big hurry and extremely determined to achieve a goal.
The “for leather” part derives from an 1889 reference to horseback riding, with the leather being the bridal and saddle.
The expression then meant “riding very fast” and began as “hell for leather.”
Hell is often used in association with speed, for example, “go like hell” or “run like hell.”