To frog-march is to make or require someone to move forward by shoving from behind. This verb is not just forcing the person to walk, but to do so roughly and with some violence. Some dictionaries go so far as to say the person being made to walk must have his or her arms pinned down or restricted.
Inside the United States, dictionaries are split between frog-march and frogmarch. However, for the rest of the English-speaking world, the verb is spelled without a hyphen, frogmarch.
In time the United States may come to a consensus, but for now, be aware which dictionary your publication values most and go with that.
Note that it is never an official spelling to break the term into two words, frog march.
The term does come from a frog being pinned down on a tray while it is being dissected. In the past the term was used for physically carrying someone out of a room, usually a disorderly person that would require being held at four points and his or her legs and arms would be spread out, like a frog.
The Met, though, lacks the abundance that enables MoMA’s linear frog-march through Europe’s unfolding art movements. [The New York Times]
However cross whatever they just did has made you, you’ll still lack the gargantuan strength needed to successfully frogmarch a recalcitrant adolescent up to bed. [The Telegraph]
They stormed into The Drink and grabbed Morrice and his friend from the dance floor, pinning their arms and frogmarching the men into a back alley. [Ottawa Sun]