Intimidation and distraction are perfectly valid strategies to win a game, duel, or fight. It might not be classy or "sportsmanlike", but every edge helps. Then again, there are some duelists who are so arrogant and smug that they'll trash talk a blue streak across the arena out of sheer pride.
During the course of a sporting event, Serious Business duel, or an armed fight, one, both or all present will start trash talking their opponents to psych them out. They'll say their two year old ADD niece is more competent, that their equipment is liable to explode before the fight starts, and they are blessed to fight someone so Magnificent that this Tuesday will be the single greatest day of their (doomed) opponent's life.
Don't expect the trash talker to lose time over it, either.
It's worth noting that like in Real Life, Trash Talk can be either harmless fun or spiteful. How Worthy an antagonist is can usually be determined by what kind of trash talk they use. If they say proud or hurtful things, they're usually bad guys, while if they 'just' say overly self confident things, like "Don't Hold Back!" or matter of factly and humbly state they are simply more powerful than an opponent, they're usually Defeat Means Friendship material, or at least an enthusiastic competitor. In especially satisfying reversals, the trash talking antagonist will say "This Cannot Be!" when the hero shows how truly powerful and/or competent he is.
Staple of Shōnen, Real Life sporting events, and series and shows that deal with a lot of fighting or dueling.
Compare "The Reason You Suck" Speech and Evil Gloating. If there's a sense of moral outrage involved, may overlap with Kirk Summation. Frequently paired with I Am Not Left-Handed. See also Pre-Asskicking One-Liner, Badass Boast, Blasé Boast, I Shall Taunt You, Taunt Button, You Fight Like a Cow, Volleying Insults, and Years Too Early. Contrast Combat Compliment. If words are enough to stop the fight all by themselves, that's Talking the Monster to Death.