@es_kan @Renan_Walheim
The color blue isn't related to football but to 'a feeling of youth', if I understand correctly. For example, you have other manga series with titles like gunjo (ultramarine blue), gunjo ni siren, blue giant, blue flames, blue orchestra etc.
This is elaborated upon in the afterword of gunjo ( https://mangadex.org/manga/169/gunjo ), though I still don't get why it is used that often.
https://braintrustmusic.files.wordpress.com/2014/05/the-more-you-know2.png