Unfortunately, you'll have to share a lot more information in order to try to diagnose the issue - it could range from one setting that was accidentally altered to a completely faulty camera on its last legs and ready to die.
If you can post a blurry sample, that would help determine if it looks like a focus issue, processing issue, shutter issue, etc. If you can note some of the settings the camera is in when you switch it to sports mode (what shutter speed did it use, what aperture did it pick, what is your ISO set to, what focus area was being used or lit up, what focus mode was the camera in, what metering mode was the camera in, etc). Even if you use a scene mode and don't set any of those things yourself, your camera will usually still tell you all of this information on the screen.
Hopefully, it's just a setting that got changed, and changing it back will fix your problem. Another thing to try is use a different lens, if you have one - see if the mode works with that lens. Make sure to try all the other scene modes of the camera, and see if they all seem to be working properly, to make sure it's just sports mode with the issue. Sometimes, you can reset your camera too - usually there's a reset button somewhere on the camera, often on the bottom, or inside the battery compartment - it's usually a very small hole you could only access with a pin or needle - or sometimes it involves a sequence of turning the camera on or off while holding down other buttons for some length of time...the manual hopefully can reveal the trick for your camera.