From the Reddit post, which indicates that it took place in Marinette, WI, and involved the NOAA Ship Reuben Lasker:
The boats normally have steel rails welded to their hulls that ride along the metal bleacher looking things when the boat is set free. After the launch these are obviously removed. However (Still assuming this is the same boat, 90% sure) with this boat design, they were unable to attach these steel rails and had to use wooden ones instead. I have a friend that works for the shipyard and basically someone made a huge misjudgment and the wood split and flew everywhere, as you can obviously see from the video. After this incident viewers were no longer allowed to be so close to the launches.
And here's more about the story behind the video.