When watching NHL I see ads on the boards. Some are static, but others are dynamic. I assume these are somehow place there so only the tv audience sees them. Otherwise they’d be dangerously distracting for the players. Is this correct?
Yes. Not only are they on the boards but also directly on the ice and change throughout the game. There is a particularly annoying one in our region that shows up in the second period where part of the logo looks like a player left their stick on the ice.
Yes, if you see the close-up shots of the boards you can see the ads that are actually on the boards rather than the the TV ads.
The main camera will usually show the changing ads in their shots. The secondary cameras usually do not show the ads.
You’ll see a similar thing if you watch major league baseball games on TV. Many of the networks which carry them will rotate “virtual” ads on the padded backstop behind home plate, so it’s visible when they use the typical camera view of the pitcher and batter, as taken from the center-field camera.
A few weeks ago, I was watching an NBA game on TV (maybe ESPN?), at TD Garden (home of the Boston Celtics). There were ads which appeared on the court (in the “corners” of the floor), which were only visible in shots from the main camera, and which changed each quarter.
Besides the computer-added dynamic ads on the boards, you’ll also see what appears to be a big sign behind each goal that could not actually be there without fan uproar. And near center ice there are some dynamically added adds that look like they’re painted along with the lines and logos.