The idiom hands down has two meanings: (1) winning with ease or with little or no effort, and (2) without a doubt. The first definition is the original. It comes from horse racing and refers to a jockey dropping his hands toward the end of a race when victory appears certain. And while the expression is mostly used in reference to sure victories, writers sometimes use it for emphasis in sentences such as,
Hands down, some of the best ramen in the city can be found on Fourth Avenue. [Gothamist]
Here, hands down means without a doubt or indisputably.
When hands down functions adverbially (e.g., hands down, he is the winner), it doesn’t need a hyphen. As a phrasal adjective preceding the noun it modifies, it takes a hyphen (he is the hands-down winner).
As an adverb
Spring Hill prison has seen it’s fair share of hairy inmates – but yesterday’s newest two residents win the title hands down. [Stuff.co.nz]
This time, though, it was actually true and Strictly Come Dancing 2011 was, hands down, the best in the show’s nine-year history. [Daily Mail]
As an adjective
Tropical Storm Irene was a hands-down winner, getting a clear 60% majority of the votes. [Wall Street Journal]
U.S. stocks were the hands-down favourites in 2011, showing the only gains among the major indexes. [Globe and Mail]