Tail Slap

There is a reason most vertebrates have tails. They can propel you through the water, free up your other limbs for multitasking, are great for balancing, can bait predator and prey alike, are good for showing your intentions and they can swat flies. Why stop there? If it works on a small pest, why not a larger one? You may not have the thumbs necessary for cracking a whip or swinging a chain, but a firm Tail Slap can be just as good.

Prehensile Tails can be flexible enough to hit things, but not all of them are powerful enough to be effective deterrents. For added power, some tails have a weapon attached - see Beware My Stinger Tail for some of those. Also compare with Combat Tentacles.

Anime and Manga

 * Dragon Ball has Goku, Korin and Freeza do this.
 * The Nine-tailed Fox's tails in Naruto are incredibly strong, sharp, and hot; they can devastate mountains and raise tsunamis, as well as pierce human flesh and leave chakra behind, which repeatedly burns and heals the affected area.
 * Meroune Lorelei from Daily Life with Monster Girl is a mermaid, and so her tail packs a similar musculature and strength to a human's legs. A tail slap from her is thus akin to a roundhouse kick, and can easily knock a man off his feet.

Comics

 * The Lizard likes to do this in Spider-Man stories.
 * This also applies to the Lizard's copy cat Komodo from the Avengers stories.

Film

 * Godzilla will sometimes attack this way in his movies.
 * Littlefoot's mother in The Land Before Time; see the dinosaur Real Life example below.
 * The raptors in Jurassic Park occasionally do this, but use their claws more.
 * At the end of Dinosaur, Aladar and Neera use their tails to attack the Carnotaurus.
 * In Kung Fu Panda, Master Viper's fighting style is based primarily around this.
 * The titular monster of Syfy movie Super Shark attacks this way.

Literature

 * Raptor Red by Robert T. Bakker uses 'whip-tails'.
 * In the Redwall series, the otters frequently use their tails as a weapon; the strongest and most skilled can knock an enemy unconscious with a single slap from their tail.

Live-Action TV

 * In Dinosaurs, the quadrupedal Monica gets a job as a tree pusher at Earl's job site. She can knock over a whole lot of trees at once by slapping with her tail.

Oral Tradition, Folklore, Myths and Legends

 * The tail is something most people forget about when depicting the Behemoth, except for those who think it was a dinosaur. Most sources depict it as an hippopotamus or a bull, animals most definitely not known for powerful tails.

Tabletop Games

 * Dungeons & Dragons:
 * During 1st Edition, a Dragon magazine article gave dragons a tail attack usable against creatures directly behind them. This was included as a base feature in 2nd Edition.

Video Games

 * Pokémon:
 * Tail Whip is a subversion, where the user wags their tail cutely to lower an opponent's Defense.
 * Tauros has whip-like tails that it uses to psyche itself up by swatting itself.
 * The Steel-type Iron Tail, introduced in Pokémon Gold and Silver, and Water-type Aqua Tail, introduced in Pokémon Diamond and Pearl, count as this.
 * Pokémon Black and White introduce Minccino and Cinccino's Signature Move (and Trope Namer). They usually use their tails to sweep away dust, but at a high enough level can use it offensively in combat.
 * Tails from Sonic the Hedgehog can defeat most enemies with a simple swipe of his tails.
 * This primarily how Gex fights.
 * This is also primarily how Croc fights, despite being a crocodile!
 * Jurassic Park Warpath makes use of the dinosaur version
 * Nearly ditto Primal Rage. Sauron (no not THAT one) and Diablo (no not THAT one) have tail-swinging blows, as does Vertigo).
 * Dragon pets in Mabinogi always finish their combo on an enemy by spinning in a complete circle and bashing the enemy with their tail.
 * In Battle for Wesnoth, the campaign unit Merman Brawlers can use their fish tails to hit and stun their enemies, slowing them. Also, the downloadable setting "Era of Magic" has the lizardfolk's Chaos Riders, who can use their Chaos Wyverns to perform a "tail sweep" at the enemies.
 * In BlazBlue, Makoto (a squirrel girl) does this in some of her grab attacks.
 * Super Mario Bros. 3 has the raccoon suit's tail as well as the P-Wing and tanuki suit. In Super Mario 3D Land, this is extended to a lot of things.
 * In La-Mulana, the boss Tiamat can whip out her massive tail to do a lot of damage to Lemeza.
 * Crocodile-like enemies in EarthBound can "swing their tail very hard" as an attack.
 * Bullsquids from Half Life possess a surprisingly powerful spinning tail-smack finisher which often reduces a victim to Ludicrous Gibs.

Web Animation

 * In The Dolan Life Mysteries episode, “If Knees Were Backwards, What Would Chairs Look Like?”, Dolan is slapped by Hellbent, Shima, and Melissa after he mocks tails.

Western Animation

 * Gary the Rat's tail is strong enough to knock a man out a building with a flick.
 * Grimlock from Transformers when not in robot mode.
 * Courage the Cowardly Dog:
 * Katz uses his tail during his handball game against Courage in the first episode.
 * Courage and Eustace use this against each other after they are turned into kangaroo monsters.
 * Whiplash in the original He-Man line. Dragons too, as people are roughly proportional to flies next to them.
 * The white whale from Moby Dick.
 * Both The Godzilla Power Hour and Godzilla: The Series feature this with the title character.

Real Life

 * Dolphins slam their tails through the water at high speed to create a wave of energy that stuns and confuses the fish.
 * Some sharks can cut a man in half with a swipe of their tails.
 * Most lizards, crocodilians and similar-bodied reptiles, even juvenile water dragons, can all do some serious damage with their tails.
 * Dinosaurs in the Diplodocus family of sauropods had long tails that apparently seem to have been whip like. Possibly other sauropods as well, they all had long, muscular tails.
 * As mentioned in the description, cattle make use of their tails to swat flies, as it can reach everywhere their head and legs do not, and has multiple ends they have trouble avoiding. They give the same treatment to farm hands they don't like.
 * Many species of catfish have tail fins (and other fins) bony enough that people will often assume they were stung by something if hit by them in murky water.