The Force Field is a dungeon tile that causes damage when a hero passes over it.
The Force Fields flicker in and out of existence. Passing over a Force Field when it is active will deal minimum yet steady damage to a hero. It does not impede a hero's movement.
These are yellow barriers that are generated by two runic plates set into the wall. If a hero travels between the plates as the yellow barrier appears, they'll take damage and be knocked down.
They're the same here as in Legends.