Hell for leather means as fast as possible. The term was first used in print in 1889 by Rudyard Kipling, specifically referring to riding a horse at breakneck speed. The leather in this case either refers to the leather in the saddle or the leather in the crop.

What does going hell for leather mean?

Moving recklessly fast, as in Out the door she went, hell-bent for leather. ... 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.

What does the phrase hell bent mean?

: stubbornly and often recklessly determined or intent hell-bent on winning.