Did they actually form shield walls? Did they actually open them up, let the enemy stream in, then turn around when the enemy was surrounded? Did they actually list up archers behind the shield wall so they could shoot over it?
Here are some threads with the same question.
https://www.reddit.com/r/AskHistorians/comments/20z05b/how_accurate_is_the_combat_from_the_show_vikings/
https://www.reddit.com/r/AskHistorians/comments/37m8j2/was_the_viking_fighting_style_as_hard_to_combat/
Also, just to clarify, it's a History Channel series, not Netflix.