Plus your enemy knows what's coming

Having lived in Japan for 3 years and experiencing a lot of their culture, I've learned that the reason anime characters yell their attacks is because it promotes a fair, honest fight. Japanese people love friendly rivalries, and the only way to truly prove yourself better than your opponent is to give them every advantage and still come out victorious. Only a truly bad person would try to sneak in for an attack and catch their opponent unprepared. And that won't settle any rivalry, even if they won the fight.

Plus, yelling your attacks just sounds cool.

So, like, I can throw a party balloon filled with 1.7 liters of urine at someone and it will be acceptable, as long as I remember to shout: DANGEROUSLY OVERFILLED PISS BALLOON as I toss it?
Alternate names for consideration: pissengan, urinitron, bakapeepee
EDIT: before you even tell me that I can't go around hucking piss balloons, remember that these people might literally poke me in my actual anus, as a prank. If someone does that shit, I'm definitely piss-ballooning them, at the earliest opportunity.
- So, like, I can throw a party balloon filled with 1.7 liters of urine at someone and it will be acceptable, as long as I remember to shout: DANGEROUSLY OVERFILLED PISS BALLOON as I toss it?
  Rules of the roads, Bubbles!
- I think that's just called Jarate and the only difference is the container. Personally I'd go for the jar, might cut them and then you're pissing in their wounds.
One punch man then is very rude when he kills the opponent mid-speech?
- He just matches whatever he's facing. Usually he has the decency to say he's gonna finish them off with Consecutive Normal Punches, or pretend like he's also going for a finishing move like Serious Series: Serious Punch.
  Many times he doesn't even try and end a challenge with a punch, it's more of a "move out of my way" smack because his mind is elsewhere.
- Nah, even japanese are tired of gloating villains now. And it's kinda funny to just cut them off.
Me when I have 4 seconds to figure out how to deal with my opponent's World Ending Nuts Kick
Sneak attack? That's like THE definition of a ninja; made in Japan
- Ninjas are typically silent assassins, not badass anime protagonists. (I'm looking at you, Naruto!) Their deeds are not generally honorable in nature. Historically, they're seen as more of an unfortunate necessity to preserve dynasties. The honorable warriors are the samurai. Although history has shown that the whole "way of the samurai" thing was actually made up for Japanese theater and they weren't historically honorable either.
  Regardless, when it comes to modern-day Japan, they love the concept of an honorable protagonist who wins by sheer willpower, even if the odds are stacked against them. Giving their opponent the advantage and then still winning in the end is seen as a clean and respectful victory.
Yeah, well, people attacking me with their wakarimasen special tends to be tiresome after a while. It's not that powerful anyway.

It's an established fact in Manga/Anime, if you don't name your Ultimate move its just not powerful.
Like even Saitama named his ultimate move "Serious Punch" and so far it hasn't failed.
My favorite is Gum Gum Bell

Pokemon world in shambles

My thought is that it helps the audience know what exactly they're doing. Not saying it's necessary because I think a good visual indication will let the audience know, but I think that's what they were maybe going for.

I really liked YuYu Hakusho for having big title cards whenever some characters would use attacks (and sometimes equipment/weapons) without yelling. It was also nice that the narrator would sometimes explain things quickly to not detract from the action, though they stopped doing that pretty early on, presumably because they assumed the audience would have a better grasp on things as the show progressed, or because the characters actually had a reason to assess or explain things.
- The ol' Brock effect, a character who's job 90% of the time was to tell the audience what was going on. More forgivable in a kids show, used to happen way too much in more adult shows too
Especially in manga.

Jujutsu kaisen lol

It does in Jujutsu Kaisen... sorta.

I like how in JJK it's a chance to create variation in power levels while also allowing an in-universe reason to expo-dump about a character's power.
It makes a shonen trope feel like these genius characters aren't just giving away all their tricks for shits n giggles. But then sometimes we just get a total lack of explanation and that's fine too because it's more fun, and the character doesn't need to (cough Sukuna)

False, the enemy is so amazed by your fucking swag that he is frozen in place. THAT's when you hit em with the kamehameha.

PUNCH IN THE FACE!!!!

I would watch MMA if one of them started doing this.
- By the time it's said, someone's landed six of them.

Go Go Gadget Anime attack

Spells may require one of three components.

an item that is destroyed in the process of casting.
a verbal utterance,
a physica movement

Except in some power systems where it does.

Hard disagree

Doesn’t count, he uses a multiplier.

Try telling that to a tennis player

My kiai says otherwise!

Jujutsu Kaisen would also like a word

Thunder breathing, first form

I'd have lost 90% of my hype if it wasn't announced

Meanwhile Saitama whispers...

consecutive normal punches

Also Tennis Players

But all the attacks are called HRRUAAGH

I always just assumed they're like magical spells and shouting the name is a requirement to cast them

i think my hero academia sorta does this? i know the protag at least has to concentrate and think in a certain way to manage to pull fancy moves off before he internalizes the activation and can really do it at will, and i think other characters have similar challenges?
"so clench your buttcheeks kid, and yell this from the depth of your heart: SMASH!"

Also, getting more emotional = more power

cries in verbal spellcasting components

JIU JITSU!!!

He's technically calling his opponent's attack there.

https://youtu.be/qXpWv-nyHvI?feature=shared

If you call out the name of your attack, you better hope your opponent doesn't know what it is, cuz it seems pretty easy to block or dodge something you know is coming.

my favourite take on this is to have characters fighting in groups, then it becomes obviously necessary to call out moves so others know what's going to happen and can know to not stand on the other side of the enemy that's about to be showered in flame.

it also makes a nice contrast between solo fighters and those who simply don't care about collateral damage: some villains can be pure chaos, you can have rogue heroes who just end up hurting innocent people because they don't coordinate, and villains who do coordinate will look way more threatening because they aren't hurting themselves.

Pocket sand!

Captain Falcon in shambles.

Tell that to Austin Powers. Judo chop!

name your attack {{{{ so the enemy doesn't know whats coming

Oh, it does! Tried it, once, very drunk, many years ago (many!), screamed something like "in your face" (actually German: "in die Fresse") and he was out cold. Only medium knuckle pain, I'm not a fighter, so I thought it did something. Don't worry, he earned it, believe you me.

Gamu Gamu covers ears.