"Hands down" is an idiom that means without a doubt; definitely; undeniably. It implies that something is so clearly the best or most likely option that there is no competition or argument. It can also be used as a synonym for easily or by far.
For example:
The origin of the phrase possibly comes from horse racing, where a jockey would loosen their grip on the reins ( "hands down" ) when victory was certain, indicating an easy win.