E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
At fault. Not on the right track; doubtful whether right or wrong. Hounds are at fault when the scent is broken because the fox has jumped upon a wall, crossed a river, cut through a flock of sheep, or doubled like a hare.
In Geology, the break or displacement of a stratum of rock is called a fault.