Stuff-ups, goofs and plot holes.
It's a common trait of mass-market shonen action pieces that their stories are full of holes, retcons and contradictions and Eyeshield 21 is definitely no exception. I'm not trying to go on a long bitch about what's wrong with the series, I just felt like collating some of the series' gaffes for amusement value. Please feel free to contribute.
By the way, don't bother listing ones from the anime. You'd never reach the end of it. The anime is so stuffed up that practically the entire thing can be considered non-canon (Monta throwing something accurately?!)
*In chapter 163, Akaba tells Sena that 'Eyeshield 21' is the name given to the strongest running back in each generation. This makes his use of the name rather silly, since Akaba himself plays tight end.
*In chapter 133, a video is shown of Seibu flattening Taiyo 60-0. Given that even Koigahama were able to score 10 points again Seibu, this is ridiculously improbable.
*In chapter 141, Musashi has an argument with his father, a conversation with his co-workers, a shave, drives to the Deimon/Seibu game and gets changed into his football gear to make a field goal all in the space of time between 2 plays. Even if the Devil Bats used a timeout, this is still impossible.
Fee free to add some more. But seriously, don't even get started on the bloopers in the anime.