Optimus Primal: You can't stop that thing alone! Tigerhawk: Perhaps... but it is my destiny to try. I will hold the line here. Go!
Then again in the Grand Finale of Beast Machines. All of the other Maximals have been defeated, leaving only Cheetor (who is surrounded by destroyed Veichons) preventing the Veichon Generals from entering the ship. Subverted in that they all just open fire on him, forcing him back into the ship. Double Subverted, as he then (somehow) hurls two of them into outer space, and takes on the last one, before removing its spark.
Cheetor: Three or 300, you're not getting in.
Codename: Kids Next Door: Monty Uno, the legendary numbah zero with a restored memory, faces his father, a meglomaniacal super evil who wants the world to be like the good old days and almost completely has done so, and holds him from reaching the last shred of the world he hasn't turned Victorian, his brother's mansion.
Monty Uno (Numbuh 0): I am not moving from this spot!
In the mid-1990s X-Men animated series, in the first season finale, Wolverine and Gambit are infiltrating a Sentinel production facility. Wolverine smells some, and so he herds Gambit to relative safety—then locks the door behind him and runs back to face them. Subverted in that Gambit blows the door open and comes to Logan's rescue. Near the end of the episode, Cyclops finds the two of them standing on a pile of destroyed Sentinels, Wolverine's shirt in tatters.
Wolverine: Next time I try ta save yer life, have sense enough ta let me do it. Gambit: What make you t'ink dere gon' be another time?
Sort of inverted in the 1986 Transformers: The Movie, where Optimus Prime, as opposed to facing down a horde of enemies, charges them single-handedly to get to his target.
Optimus Prime: Megatron must be stopped... no matter the cost.
In Star Wars: Clone Wars, Shaak Ti stays behind to fight off thirty-something Magnaguards, to give the other Jedi and the Chancellor time to escape. It's then subverted when the robots stop fighting and leave, and Shaak Ti realizes too late that they were a diversion.
Happens every episode in the first season of Code Lyoko, as the usual plot involves the gang evenly matching (or being overwhelmed by) XANA's programs while Aelita gets to the Reset Button.
Parodied on Chowder, when Mung and Shnitzel are guarding the fridge to keep Chowder from sleep-eating the entire kitchen. Mung even yells out "YOU SHALL NOT PASS!" before Chowder (now a hairy, hulking thing) chews the two of them up and spits them out.
Parodied in "The Return of the Fellowship of the Ring to the Two Towers" episode of South Park; Jimmy, who has a speech impediment, stays behind to hold back a horde of bicycle-riding Sixth Graders, but due to his stammer, he can't quite get the line out;
Jimmy: You shall not p-puh... You shall not puh-puh-p-p... You shall not puh-pah-paaa— (a dozen sixth-graders run him over) Jimmy: ... Pass.
And parodied within a parody on Family Guy: in the "Petergeist" episode, Herbert the pedophiliac neighbor defends Chris from the carnivorous tree, "Hey skinny-britches! That there's my man! Why don'tcha pick on someone your own size!" He then declares, "YOU SHALL NOT PASS!" striking the earth with his walker and splitting open the ground beneath the tree - and himself. They plummet together toward the bottom of the chasm with Herbert battling the tree with his walker the entire way down.
Vector Prime: Hold, Megatron! You shall go no further! (dark clouds temporarily fill the sky overhead; a swirl forms, and from it descends a streak of green light; the light enters the socket located below and in front of Vector Prime's chest orb, and becomes his Cyber Key) Vector Prime:CYBER KEY POWER! Optimus Prime: By the Allspark of Cybertron! Megatron: What is it?! What are you protecting?! Vector Prime: Tachyon shield!
Megatron collides with the shield, and is stopped cold. Soon enough, he recovers slightly and begins trying to break through. Vector Prime responds with a laser blast from his chest orb. Optimus follows up by transforming to Super Mode and blasting Megatron as well. Megatron's shoulder badly damaged, he and Starscream retreat.
Dug in Up attempts one of these when Carl and Russel are fleeing the dogs. Dug being who he is though, his plan consists of planting himself in front of the oncoming horde and saying in a stern voice, "Stop, you dogs!". It doesn't work.
Parodied in the new Comedy Central series Ugly Americans with Gandalf the receptionist of the wizard's guild. You're free to pass, if you sign in first.
Mai and Ty Lee hold off prison guards and finally Azula to allow Zuko to escape The Boiling Rock.
The Legend of Korra continues with Lin Beifong taking out an airship and causing another to retreat in order to give Tenzin and family the chance to escape.
Jonny Quest TOS episode "The Dragons of Ashida": Race Bannon volunteers to stay behind and distract the title dragons (sort of like huge monitor lizards) so the Quests could escape. He manages to take out both dragons through clever actions and escapes.
The Teen Titans try this in the season 4 finale against Slade and his army of fire demons. Cyborg even shouts "No one's getting in here!" Unfortunately, against an immortal foe with an infinite supply of reinforcements, their defeat was pretty much inevitable.
In Transformers Prime, Ratchet, Bumblebee and Bulkhead pull this on Megatron to prevent him from getting through the space bridge while Arcee and Jack are retrieving Optimus' memories from Vector Sigma.
In American Dad!, Debbie and her Goth clique does this for Steve as he and his friends flee from the other school cliques (in a random homage to The Warriors). Their strategy is to block the enemy's progress through dancing to Joy Division. It works.
The situation is grim in Green Lantern: The Animated Series. The Big Bad is on his way to massacre the Guardians with his armada about to enter Guardian-controlled space. Hal and Razer race to stop him while Kilowog stays behind to hold back the armada.
Kilowog: ''It may only be a matter of time, but I'm not gonna make it easy for you poozers!"
He's joined by Saint Walker and Mogo.
Invoked in the Bugs Bunny cartoon "Ali Baba Bunny":
Caliph: Guard well this treasure, Hassan, or the jackals will grow fat off thy carcass.
Hassan: No one will pass Hassan!
My Little Pony: Friendship Is Magic: Shining Armor pulls this in "The Crystal Empire, Part 1" to delay King Sombra. He survives, but he ends up with magic-blocking dark crystals stuck in his horn.
Kim Possible: Performed by Monkey Fist in his debut episode while in disguise as an ordinary ninja (as part of a ploy to keep Kim from suspecting he stole the artifact "the ninja" absconds with). At one point during his martial-arts duel with Kim, -still not speaking- he draws a line in the dirt between them with his toe, glaring at her with slitted eyes as if to say, "Bring it on."
Scooby-Doo! Mystery Incorporated: In "The Midnight Zone", Cassidy stays behind in the undersea base to keep the doors open long enough for the Moby Dick to escape and hold off the killer robots.
Exosquad: Has a number of examples, this being an animated war drama. One throw away background character named Zandowski attacks a an entire enemy squad to buy time for his escaping comrades. He's repeatedly hit, and told to pull out but instead screams "No can do Admiral! You'll have to Court Martial MEEEE!" and self destructs, taking some mooks with himself. The more spotlighted character have even more dramatic deaths and heroic last stands.