This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Eyeshield 21
One of the earliest examples was a flashback to Kurita's 10 grade year. Expecting many people to try out for the American football club he bought 100 cream puffs to share with others, when not ONE person came, he was forced to eat them all alone in the dark.
Just as Unsui thinks his hard work has finally paid off, he's told that the scholarship award he'd always been aiming for was meant for his brother. The scene is made all the more heart breaking when he, in tears, declares he's going to do all he can to make his BROTHER the best, making it clear he no longer sees his own worth. Even Agon, who pretty much nicknamed him shit, doesn't find it funny.
When Devilbats lost to the Gunmen. Suzuna, unable to believe what she's seen, stammers: "this is a joke, right...? Hey... Hey...." and tears begin flowing from her eyes. It's just the beginning.
Chapter 245... "Nothing good ever comes from chasing your dreams..."
The Devil Bats apparently lose to Shinryuuji when Kurita is unable to get in place for the next set in time after a desperate long-bomb play. Especially painful after Agon's mocked him for being fat and slow the entire game. Changes to tears of joy when the Devil Bats get one last chance because of CATCH MAX!
Habashira Rui breaks down because his team chooses not to continue a losing game, starts crying to Hiruma because the two of them are Not So Different, but he's managed to surround himself with real friends who are just as dedicated to the game as he is.
Made worse by the fact that has Habashira breaks down we see flashbacks to Hiruma practising with all his friends...while Habishira threatens one of his own players with a knife and his girlfriend, Megu, stands around the corner looking very sad and dissapointed in him. See for yourself.
Actually, we also see hiruma threatening his own team with a GUN, showing that he really is not that different. Megu looks more sad and understanding than dissapointed in him. The real difference is more the fact that sena&co are genuine nice guys, who ended up earning hiruma's respect and thus forged a true friendship whereas harahibara's teammates are just spineless delinquants. It thus gets even more tragic since it means that it was only luck that decided it. Hiruma was lucky enough to meet sena&co, rui was not.
That panel wasn't a flashback. Megu is around the corner, listening to Habashira cry, and fighting off her own tears that he couldn't achieve his dream.
Apollo, of all people, when he sends Panther out because he reminds him of his non-playing days in the NFL.
When Monta doesn't make the baseball team, and makes a promise to his idol that his catching expertise will go to football instead.
Taki, realizing he hasn't done anything that great since he joined despite what he has thought, uses his flexibility to overcome the tackle-technique used by the enemy.
When Yukimitsu, who has completed the Death March, was passed over for still not being good enough to play. Sure, Hiruma was only saying that to keep the others from questioning his permanent bench status before he was needed,but his reaction later... this troper cried Manly Tears.
The scene between Marco and Maria after Hakushuu loses to Deimon, and Marco realises that in trying to win Maria over he's really driven her away. A Manipulative Bastard and dirty player he may be, but you still feel for the guy.
An earlier flashback, from Maria and Marco's joint perspectives is just as bad. They give you the buildup, and how hard the two of them tried to build a team...and then it ends with this shot of Marco, all alone.
Gao. Broke. Hiruma's. Arm. If seeing that Magnificent Bastard reduced to an injured casualty doesn't break you, everyone else's honestly distraught reactions will. Made worse during his inner monologue because he realizes it's an inner monologue, he is trying to speak but no voice comes out.
The flashbacks during the game against the USA, showing the fracturing and collapse of Agon and Hiruma's tentative friendship. Agon is left with this sense of having lost something, even as his own sociopathy prevents him from being able to understand what.