In a manga I found the following sentence:
The person to which the word タコ refers to is a secondary character that rarely appears. His name was never mentioned before. Since the person that is talking is a quite rude old man and since the word is written in katakana, I am wondering if タコ is just the name of the secondary character or if it is an offensive word like バカ or アホ。 Thank you for your help!
EDIT: Since there were conflicting answers, I decided to provide more context. Here you can see the two pages where I found the term. They are from a manga about boxing called "リクドウ", where Riku is the name of the main character. In the first page the secondary character is worried about Riku starting the 2nd round, since he almost got ko in the 1st, at which point the old man, which is Riku's trainer, tells him "ひき戻すな、タコ". The second page is right after the end of the match. It looks like the unnamed secondary character is the trainer's helper.