This is probably the most used yet least understood trope whenever an author wants their character to look cool by letting their protagonist is fight against a world that seems to look down on him. I guess you could say it's not that people can't write this trope well but that some popular media like Chivalry of a Failed Knight tend to mix the perception of what an Underdog actually is.

What I mean by this trope being the least understood is that writer's tend to give the main character a secret power yet still make it that no one accepts the user's power. I won't be giving any examples of this in particular since that will just make you guys not want to read those stories but I feel people miss the point of the trope.

An example of an Underdog done right can easily be found in a popular Anime most are familiar with: Naruto. Most think that having a kinda evil demonic fox sealed inside of them that not only makes them an outcast of their village but also makes him prone to almost being possessed by berserk power is pretty swell... At least that's what I think when I see people criticise Naruto for not being a good Underdog despite ticking all the boxes for it.

He is looked down upon by his village and is considered an outcast that no one will believe will succeed in life. Then his journey throughout the story proves them wrong until he finally defeats Pain and sheds his status as an Underdog who is not really that much of a powerhouse. From there the story continues with a matured Naruto that can make full use of his inheritance and abilities.

One thing Author's have to make sure about when writing an Underdog is that the reader should never be put into a sense of security and must always think that the main character might not be able to win battles. Sure, he can win the war by making sure his opponent doesn't achieve their objective, but the main character himself has to be weak enough that the reader might think that the protagonist won't be able to win.

Don't take Chivalry of a Failed Knight or Food Wars as an example of this since they actually AREN'T Underdogs! What these character are could be considered more like 'Overdogs' that actually DO excel but aren't accepted by their peers.

Ikki himself can essentially completely predict his opponents actions (Perfect Vision), copy swordsmanship just by looking at it (Sword Steal), and other superhuman feats despite having 'Low Talent' as a Magic Knight with low grades.

You could say the best way to write an Underdog isn't focus solely on battles themselves but how the character himself doesn't seem likely to achieve whatever he set as his goal. If he wants to be the best pianist, make him a beginner that will have have to contend with more experienced musicians. This example can be spun in a number of different ways. As long as the main character isn't a genius, then a Underdog can build tension.

For a more recent example of a great Underdog written in shonen, look no further than Kimetsu No Yaiba. It is a masterfully written work that build tension since the main character is usually almost always outmatched by his opponents, the only way he is able to is by getting help from his friends and making use of everything at his disposal as a combat pragmatist. He doesn't have the leisure to be 'chivalrous' and always cheats to the best of his ability to defeat foes that are after his life.

It would be a lie that there isn't any stakes in this story due to the realism it incorporated into its almost too 'normal' power system. The protagonist doesn't instantly heal from injuries by the next arc and has to keep track of a number of things like his blade's sharpness and his own ability to survive the deadly encounters he has no control over.

Although no one is looking down on the main character other than some of the higher ups of the organisation he joined after finding out his sister's a Demon (not really a spoiler since it would eventually happen anyway), the reason he is a perfect Underdog is because there is never a sense that the main character will be able to steamroll his opponents if they were to meet.

In fact, humanity as a whole could be considered the Underdogs of this series since they are fighting near immortal monsters of the night that really don't allow them to pick the time or place they will fight. No character is safe and there's no undisputed powerhouse on humanity's side that can beat the big boss they are aiming to kill.

But enough of me gushing over how cool this series is, my main point is that Underdogs can be done wonderfully not by constantly throwing tragic events at the main character but showing the optimism that the protagonist can STILL reach his goals even if it's not through regular means.

An Underdog doesn't have the complacency a powerful character can have, only the drive to work hard to fill in what he's unable to do himself or through asking for help from those around them. I know it hurts the pride of capable main characters to ask for help, but an Underdog doesn't have the leisure to let his get in the way of his goals.

It is only natural a character that is underpowered to ask for help when in need. In fact, once he gets enough power, a writer can show just how the main character has matured by allowing him to complete a task he was unable to do weeks or years before.

Character development is key. And the most important thing a writer should consider when about to use this trope is if they are going to make his status as an Underdog permanent or allow him to grow enough to grow out of this trope.

If they just constantly make the story about the MC being unable to do anything about his situation if there's at least one percent chance of him growing out of the trope, then all the readers will see is a Tragic Protagonist rather than an Underdog.

Trope safely and I wish you all the best of luck if you're going to use this in your story~ ?