A taller character is being attacked by a shorter character and does one of two things:
Plonks a hand down on top of the attacker's head and holds him at greater arm's length.
Picks up the attacker up holds him arm's length.
This is more common in comedic situations, or other situations in which a humor is preferred to a merciless beatdown.
This works best on characters who are flailing in a panic or incoherently furious, since it holds them safe until they can calm down. It becomes less effective if the person realizes they can just hit the restraining arm. Or duck under the hand. Or take advantage of the fact that legs tend to be longer than arms...
If you're looking for the webcomic of the same name, click here.
Naruto: Itachi's "finger-to-forehead" flicks he gave to little Sasuke.
Played straight to type in Macross Frontier, complete with attempted windmill punching, with the only variation being that the character being held at bay is at other times capable of stepping on the offender.
Subverted in Fatal Fury 2: The New Battle. Krauser lifts Terry Bogard up by the head and Terry's immediate reaction is to try to pry Krauser's hands off (To be fair Krauser also threatened to crush his head) His second attempt is to kick Krauser in the face, which is blocked. Finally, Terry knees Krauser's elbow, finally forcing him to let go.
Happens to Pretty Sammy in the fight against "Team Lovely Madams". She can't reach even though she's swinging her magical baton.
In Fruits Basket, a group of gangster girls try to attack Uotani (a former gang member herself) to build their reputation. Uotani hardly pays them any attention until the group's leader tries to punch her... at which point Uotani employs this trope. When the attacker is confused, Uotani even lampshades it by pointing out their height difference means that she has longer arms. She then proceeds to lecture the girls on how pointless gang life is, and how they should grow up and actually do something useful with their lives.
In Ricky Gervais stand-up show Animals, he uses this scenario as a metaphor for the Falklands War. As the Argentinian guns had a range of 10 km and the British guns had a range of 17 km, the British ships "parked 11 km off the coast and bombed the crap out of them." Gervais described this tactic as "the military equivalent of holding a midget at arm's length and kicking him in the bollocks."
In the short story Winterfair Gifts, SGT Taura described how she invokes version two of this trope when on bodyguard detail and simply looming (she's 8') or smiling (her fangs are scary even when she is not trying to be intimidating) do not make someone back down.
In Exiles of ColSec, Cord (who's not stated to be taller than the other character involved, but is definitely bulkier and stronger) intervenes in a potential squabble between Jeko and Heleth by doing this to Jeko.
Subverted in an episode of Extras where Andy tries this when Warwick Davis attacks him and he punches him in the wrist. Andy says it works in cartoons.
Happens hilariously in an episode of House, where the eponymous character is keeping Taub away from the latter's phone while texting Taub's wife to take her clothes off.
Subverted in the Halloween episode of Honey, I Shrunk the Kids. Amy's boyfriend Ray does this on Nick, but Nick punches him in the stomach.
A The Kids in the Hall sketch has a lazy thief robbing a lazy man whose idea of self-defense is to hold out his hand so the robber can't reach him. It works as the thief walks right into the hand, twice, and then uses his "street smarts" to simply brush the hand away.
Happens in the Music Video for "It's a Hit" by We Are Scientist, which depicts the band as 1920's boxers.
Jefferson implies this will be the outcome if Adams tries to make him write the Declaration of Independence "by physical force" in 1776.
Avatar The Last Airbender: Toph does this to Sokka. Unusually, Sokka is actually the taller and longer-limbed party, but Toph was keeping him from taking back his club, which she had in her other hand, sticking out in the opposite direction.
In Dexters Laboratory, Deedee does this not only with her arm, but with her leg, putting her foot on Dexter's forehead. He's just that short.
Frequently done by Mr. Krabs in SpongeBob SquarePants, when his microscopic business rival Plankton attempts to steal the Krabby Patty secret formula. Instead of holding him at arm's length, however, Krabs simply picks him up and tosses him bodily back to the Chum Bucket — sometimes by creative means, such as blowing him through a straw.
In the Classic Disney ShortA Knight for a Day, Cedric uses a makeshift lance made from a sword handle and the arm from his suit of armor to hold back Sir Cumference when he brings out his sword. It's an interesting flip-flop considering Cedric is the small and vulnerable protagonist, pushing back the hulking Sir Cumference.
Aqualad does this to Beast Boy in Teen Titans. Eventually, Beast Boy stops flopping around and just swats Aqualad's hand away.
Wakfu gives us the lovers' spat variant. Evangelyne is held at bay by Sadlygrove as he's reading her diary, which she'd written while thinking he was dead — and thus is saying way-too-nice things about him to Eva's taste.
Subverted in real life.
Try it; the short kid will attack the arm on his head.
Or they'll just kick. Which is when you use your leg to keep them at bay and end up hopping around attached to a small bundle of joy.
Or they fall over when running into the hand. It's effective at least, but doesn't happen the way the trope describes.
If the short guy is at all a martial artist, the tall guy had better prepare for a joint lock.