You’ll definitely need one of these. In the interest of getting the sharpest images possible, you’ll need to use a tripod or monopod. Most sports require at least 300mm long lenses which are super heavy and impossible to hold steady.
You will also find that camera shake becomes a lot more of an issue when you start to use long focal length lenses. A good tripod with an easier to use head or a monopod fixed to the tripod collar of your lens will help solve these problems.