The glowing hockey puck, yellow first-and-ten line and virtual ads in football and other sporting events may all sound kind of narrow in scope (not affecting all of television), but they are breakthrough technologies that took a ton of technological know-how. The glowing puck was introduced first by Fox in 1996 during the NHL All-Star Game. Sensors were put on the cameras and throughout the arena, and the hockey puck transmitted signals so that the puck could be tracked in real time. A glow was superimposed for home viewers to help them follow it, and when the puck moved, a directional streak in blue or red appeared on screen to show the path it took. Though a technological marvel that took lots of money and tons of computing power -- and engineering know-how to pull off -- it was widely panned by fans of the sport. The furor over the technology seemed to up the ratings, but the glowing puck was discontinued within a few years.
The similar first-and-ten, aka "yellow line" -- introduced by ESPN in 1998 and developed by Sportvision -- was much better received, perhaps because it solved a real problem and was more unobtrusive. It even won an Emmy. Home television viewing audiences had trouble discerning the first-and-ten line, which was marked by poles held on the edges of the field. The technology's ability to "paint" the line on multiple shades of green grass, while excluding the colors of the teams' uniforms, make it really look like something painted on the ground that the players are stepping over. As of 2003, it was added to Skycam video so that replays could also have the line. The first-and-ten line is still in use today at ESPN and has spread to other networks in various forms.
Similar technology is also used to impose virtual advertisements on the fields and other parts of the sports arena (but not on people, as this is forbidden).