hell-bent for leather

Moving recklessly fast, as in Out the door she went, hell-bent for leather. The use of hell-bent in the sense of “recklessly determined” dates from the first half of the 1800s. Leather alludes to a horse's saddle and to riding on horseback; this colloquial expression may be an American version of the earlier British army jargon hell for leather, first recorded in 1889.