A hands-down victory is one that is so assured that a jockey can drop his hands and relax his grip on the reins as he approaches the line.

I got this from Maven's word of the day.
A coworker used the phrase "hands-down choice" in some marketing material, and we wonder about the origin of that expression. I guessed it had to do with parliamentary procedure, and he speculated it had to do with card games. Its origin seems neither easy nor certain!
There are a number of plausible explanations for the phrase hands-down, which means, as you note, either 'easy' (a hands-down victory) or 'unquestionable; certain' (the hands-down choice for the office) (or as an adverbial use of either of these, e.g. "He won hands-down").

The hands-down origin of the word, however, is from horse racing. A hands-down victory is one that is so assured that a jockey can drop his hands and relax his grip on the reins as he approaches the line.

The phrase is first found in the late nineteenth century. The two earliest examples are literal references to horse races, which makes pretty clear the notion that this is the origin.

http://www.randomhouse.com/wotd/index.pperl