Force field

Although this article is based on canonical information, the actual name of this subject is conjectural.

“Enemies, fly and fall... Circling arms raise a wall!”

―Willow Rosenberg

Willow creates a force field to protect herself from a Grimslaw Demon

A force field was a solid barrier conjured mystically and used to protect a person, object or whole area.

Examples

• When Willow Rosenberg's essence was combined along with Buffy Summers, Xander Harris and Rupert Giles, Willow cast a spell that blocked Adam's bullets with an invisible shield that vaporized the bullets as they made contact.

• Willow used a spell to contain Glorificus inside her apartment, creating an invisible wall that would vibrate as Glory touched it, literally thickening the air around her. She activating it by saying "Thicken".

• Willow cast a spell that created a force field big enough to cover a gas station where she and her friends were held up to protect them from the Knights of Byzantium. While the Knights used clerics to try to disable the barrier, Glorificus was able to punch a hole into it to let her pass through before it mended itself while Buffy needed Willow to create a "door" in the force field. According to Willow, this spell would only last for half a day, and was in a fixed position, so it couldn't defend a moving object.
• Months after her decent into darkness, Willow angrily created a force field to protect herself from a pouncing Grimslaw Demon.
• When a Turok-Han vampire hunted after Buffy and the Potential Slayers, Willow tried to hold it off with a spell to conjure a force field but could not keep it up as the ancient vampire was too strong. However, Dawn Summers speculated that Willow intentionally let it fail. 
• When magically transformed into Warren Mears physically and psychologically, Willow created a force field to prevent Kennedy from accompanying her.
• All vampires were prevented from entering human residences by an invisible wall without an invitation from the owner or simply a resident, so long as they were alive. This also extended to single rooms if the person residing there lived in it as if it was their own private residence, separate to the building containing the room. If the invitation was granted, then the vampire could enter the home as they pleased unless the proper ritual were preformed.
• An invisible barrier was created after an earthquake disrupted The Master's attempt to open Hellmouth beneath Sunnydale, imprisoning the Master, and the Master only, in his lair for sixty years. Every time he touched it, the barrier would vibrate rapidly. It was only until he drank the blood of the Slayer that he could break the barrier open, resulting in a bright light shining for a short moment.
• The Box of Gavrok was protected by a small mystical barrier while in the Mayor's possession. While staying unseen, touching it would cause it to become visible.
• All enslaved demons wearing a XXI's Bracelet were confined to an area designated by a red line. Crossing the line meant disintegration.
• The cavern lair of Nezzla Demon was protected by a barrier that only they could cross and split the intruders. Only those wearing their skin were allowed to cross the barrier. Jonathan Levinson made it possible for Warren to steal the Orbs of Nezzla'Khan. 
• After his capture by Angel for to interrogate on the possessed Cordelia Chase, the demon Skip was standing inside a cylinder of red light generate by a circle of red palm sand.
• The Immortal's bodyguard use a force field for to prevent Angelus and William the Bloody to enter at his party.
• Willow cast a force field over Santa Rosita to control the zompire outbreak.
• In their dimension, the Nitobe demons have a jail system using an energy barrier. It was here that Eldre Koh was emprisoned until Buffy Summers destroyed the seed.
• When Rupert Giles was resurrected as a child, he conjured a forcefield to protect himself and the other scoobies from a crumbling building.

Force field spells

• Sumerian Defense spell
• Force field spell 
• Protective Barrier spell

Countermeasures

• The dissolution spell could break down force fields.
• The immense strength of certain beings like Glorificus and a Turok-Han vampire could break apart force fields. 

Gallery

Behind the Scenes

Force fields make an appearance in the Buffy the Vampire Slayer Xbox game.

• Hanoch and Siren demons could create magical barriers that would close only after they die. 

• Urd could protect himself with a small force field that destroyed projectiles and electrocute any enemies that touched it. 

Appearances

• "Welcome to the Hellmouth"
• "Prophecy Girl"
• "Bewitched, Bothered and Bewildered"
• "Passion"
• "Lovers Walk"
• "Choices"
• "The Prodigal"
• "The Ring"
• "Primeval"
• "Real Me"
• "Untouched"
• "Crush"
• "Tough Love" 
• "Spiral" 
• "Seeing Red"
• "Selfless" 
• "Showtime" 
• "The Killer in Me"
• "Inside Out"
• "The Girl in Question" (Only in flashbacks)
• "New Rules, Part One"
• "United, Part Two" (Only in flashbacks)
• "Love Dares You, Part One"