Not only is it not against Judaism, but I think it’s something that can be quite positive and helpful in living a Jewish life.
Surprised? Let me try to explain.
First of all, although there isn’t any competitive sport in Jewish history (until modern times) or even any teachings regarding competitive sports, they indeed play a role in modern society to allow people to relax from modern life’s many pressures. Nowadays, playing or observing a sporting event serves as a “kosher” means for an enjoyable experience with one’s family and friends. This need today is vital for most people to enable them to manage their daily grind of fulfilling their obligations without becoming depressed and finding it difficult to fulfill their potential to live a fully Jewish life.
That’s how I see the benefit of sport in general. I personally know many religious Jews, including Rabbis, who both play sports and go to games in their spare time.
But what about rooting for a specific team as you asked? It might even seem absurd. Why should I care which team wins? How does the outcome of a game really have any effect on my life? As strange as it may sound at first, I feel that the idea of rooting for a team can be positive for a person in being successful and happy in many aspects of life.
How is that? Psychologically, a person who is personally involved in something, or “sees himself” as part of something, then his nature is to be more interested in whatever he’s doing. He identifies himself with it. Since he feels a part of it he will be a more positive experience for him.
For example, if a person is learning some topic of Torah and has a question and asked his teacher the question (or sends the question to Gateways’ Ask the Rabbi!) he will be more likely to remember that subject and what he learned from it with greater clarity and depth. Why? Because he sees himself as an integral part of the subject matter that he’s learning. It’s not just an academic matter that is separate from him. Since he’s asked “his” question he feels a part of what he’s learning – the learning experience is not just some “removed” information. It’s personal, will have more meaning to him and he will remember it better.
One final thought. Of course don’t be too heartbroken if “your” team loses. It’s only a game.