Misplaced Retribution

Some retaliation exceeds what's being retaliated to in its severity. But some retaliation isn't even along the same line; it's directed at those who can't reasonably be blamed for what you're retaliating for, except according to exceedingly shaky justifications. Whether it is worse than what is retaliated to or milder, the point remains that it is still indefensibly directed at the wrong targets.

Closely related to Misblamed, and a Sister Trope to Revenge by Proxy. It's one of the many ways in which a Cycle of Revenge can get ugly. Avenging the Villain is also related, since The Hero (or whoever killed the villain) is usually either blameless or justified.

Truth in Television, of course. From a psychoanalytic point of view, this is called displacement, and occurs when someone who feels under attack emotionally retaliates against someone who is a better victim than the aggressor - for some reason, it is more viable to emotionally attack this new target than the aggressor.

Examples of Misplaced Retribution include:

Anime and Manga

In The Breaker Manhwa, a great deal of characters are after Han Chun Wo, also known as Goomoonryong, because he killed their master or performed some other dishonorable thing upon their martial arts school. He is a complete and utter Badass upon which they have no hope of carrying out their revenge. Therefore, they prefer to target his student, Yi Shioon, which becomes particularly unfair and messed up in The Breaker: New Waves when Shioon looses his ability to use ki and becomes completely helpless, is renounced by his Master as a student and is no longer a Murim (part of the martial arts world) and should be off limits.
This is played with in Axis Powers Hetalia. Canada is frequently the target of this because he looks almost identical to his brother America, though the countries that are pissed at America wouldn't harm Canada if they knew the difference. That he's very soft spoken means he rarely is able to stop the abuse or convince the other countries (rightfully angry at America) from beating up on him.
This is part of the reason why Master of Martial Hearts has one of the worst endings to an anime ever. And they didn't even manage to get back at the intended target.
A particularly bad example in the case of the anime-exclusive villain Valgaav from Slayers; he was subservient to Gaav, one of the world's five Dark Lords, and he goes on an all-out vendetta against Lina and her comrades for killing him. Problem? Another Dark Lord, Phibrizo, killed Gaav, whereas it took a massive effort for Lina and co. to stand against him.
Sasuke Uchiha of Naruto is aiming for this, which really shouldn't be a surprise, considering he's a master of Revenge That Surpasses Any Basic Reasoning.

Books

In Harry Potter, Severus Snape took out his hatred for James Potter on his son Harry, usually being stricter towards his actions then any other student.

Comic Books

One Green Lantern story's antagonist was the Aerialist, who was under the delusion that someone at Ferris Aircraft had murdered his beloved (death was in fact a freak accident) and therefore sought revenge against the company. Notable for being one of the few times Hal Jordan thought the Insanity Defense would actually work, even citing the M'Naughten guideline.

Film

This is Two-Face's deal in The Dark Knight. Rather than the Joker who actually orchestrated his tragedy, he goes after everyone who was involved in the events, no matter how weakly or by how many degrees of separation, even to the point of threatening Gordon's son.
In Star Trek: Nemesis, Shinzon directs his hatred of the Romulans towards Earth for reasons which only make sense to the screenwriter. It's never even explained what bizarre line of reasoning led to him wanting to destroy Earth and not, you know, Romulus.

Live Action TV

In a mid 90's episode of Grange Hill a guy and a girl try to escape from a fire by climbing out of a window. She slips, falls to her death, her boyfriend blames the guy who was with her and spends the rest of the season stalking and harassing him. He eventually stops and apologizes (possibly since everyone was against his vendetta).
In Law and Order UK, Matt Devlin is killed in a drive-by by a young man looking for revenge on the police for botching the murder investigation of his brother, a screw-up he believed was racially-motivated. Problem is, not only was Matt, not a bigot, he had nothing to do with the case (and probably would've been steaming mad about it). What's worse, the killer had an idea of actually pulled the trigger (a local drug dealer who may have been lying to gain street cred)--why not go after him or one of the cops who DID botch the case?
- The Mothership version of this case had a similar misguided attack, but there, the perp was much younger (14) and the victim survived with an injured arm.
Speaking of Law and Order, you can also count Jack McCoy's zealous prosecution of a drunk driver who killed three people. Reprehensible, certainly, and fully deserving of a harsh prison term. But it soon becomes obvious that his actions are motivated by the fact that the drunk driver who killed his lover Clare received a light sentence.
Cold Case: A young boy is horribly abused in a group home. So when he grows up, does he track down those who abused him and those who let it happen? No. Instead, he selects completely innocent boys who bear only the vaguest resemblance to his former tormentors and kills them, putting them through the same abuse he suffered.

Video Games

In Ar tonelico II: Melody of Metafalica, Luca for the longest time holds Lady Cloche responsible for the death of her younger sister. Cloche could not realistically have been responsible for that, considering she was only six or seven years old at the time and even though she's the head of state now, she has always been a puppet ruler who never made any real decisions. And even more so because Lady Cloche IS Luca's sister.

Western Animation

In the Invader Zim episode "Battle of the Planets", Tallest Purple orders someone Thrown Out the Airlock for not remembering Zim ruining Operation Impending Doom I. His response afterward:

"That was the wrong guy but... that's okay! I think everyone gets the point!"