"NSFL" tends to mean "Not safe for life". Usually people will use this labeling clips of extreme violence/gore/other conent that may be disturbing to observe in any context.

Generally "NSFW", meaning "Not safe for work" is used to warn that an image or video might include improper, sexual, or otherwise inappropriate content that people may want to avoid while at work, but is probably not disturbing. I think that this is a better tag for this clip (though I am not sure as I haven't watched it, I'm at work 😅).