Which manga do you think was seriously butchered whan adapted into an anime series? Simple as that.
I came up with the question after watching a couple of Eyeshield episodes. That series was not just terrible, it's an insult to the original and to the viewer.
The art is so bad even I could do better, animation even worse, there are numerous fillers and even the story itself is altered, voice acting is terrible, proper use of music non-existent and sound effects in general make babies die in their cradles (goes for One Piece too, ever paid attention to Zoro's swords' metallic sounds or clenching of fists? Oh god). Seeing as how well-drawn and done the manga is, this shit is just too much.
Don't watch it.