How can Xfinity continue to deliver live TV RT hat it as set top boxes can’t decode cleanly?

Whenever I watch sports, like football, soccer, golf, basketball, whenever the best action occurs, the decoder can’t handle the higher bit rate data streams. Whenever there is action I really want to see. I get blocking artifacts that make it impossible to see. I’ve recently replaced my set top box which produced no improvement. How can Xfinity continue to offer service that it can’t deliver?