The first thing you need to think about when writing an effective thesis statement is to determine several reasons why you think sports are bad. Because the thesis of the essay is the main idea of the entire essay, it should focus on the reasons why sports are bad and then outlined why in your body paragraphs.
For example, sports are expensive to participate in, sports are physically dangerous, and sports are not as important as academics.
Next, using those three topics or reasons why sports are bad, write your thesis.
Participating in sports is bad because _____(reason #1)_________,
_____(reason #2)___________. ______(reason #3)_____________.
I like to encourage my students to avoid just “listing” the reasons why in their thesis. Although there is nothing wrong with it, I like my students to try to be more sophisticated when they write their thesis statements. So, instead of just listing, think of ways you can say the same thing but in a more general way.
Ex. Participating in sports is bad because of the physical and mental strain it puts on the athlete. Then, in your body paragraphs, you can discuss the three physical and mental reasons why sports are bad.
As a formula, a good thesis statement will state the main idea of the topic and add a how or why reason. Sports are bad (main idea) + because (how or why reason) . . .