On Monday, several YouTube users had their videos removed from the service due to YouTube's restrictions on animal fight footage. This was confusing, because the videos in question showed no animals fighting; instead, they showed robots battling.

Robot combat has been around ever since Marc Thorpe launched the inaugural Robot Wars in San Francisco back in 1994. It has become popular around the world through shows like BattleBots in the US, Robot Wars in the UK, and the more recent King of Bots in China.

The big televised events usually showcase heavy (200lb/80kg+) bots, but those competitions are infrequent, so smaller weight classes have become popular. These classes require less money and less arena space, and some of the more popular events feature small bots in the "insect weight" classes (150 grams for Ant [UK]/Flea [US]), 1 pound for Ant [US], and 3 pounds for Beetle). Naturally, builders like to record and share videos of these robotic tussles.

On August 19, some of the smaller robots builders received an email from YouTube accusing them of uploading animal fight videos.

One such message (shown as an image above) reads:

Your video was flagged to us for review. Upon review, we've determined that it violates our guidelines, and we've removed it from YouTube. We know that this might be disappointing, but it's important to us that YouTube is a safe place for all. If content breaks our rules, we remove it. If you think we've made a mistake, you can appeal, and we'll take another look. Keep reading for more details. Video content restrictions Content that displays the deliberate infliction of animal suffering or the forcing of animals to fight is not allowed on YouTube. Examples include, but are not limited to, dog fighting and cock fighting.We review educational, documentary, artistic, and scientific content on a case-by-case basis. Limited exceptions are made for content with sufficient and appropriate context and where the purpose of posting is clear. Impact on your account Please note that this removal has not resulted in a Community Guidelines strike or penalty on your account.

Some creators were not so lucky, and they received notices giving them a strike.

Paul Sinn, a West Coast robot builder who has been competing with his family since 2010 as "House of Sinn," had 31 YouTube videos taken down. This resulted in two strikes against his account, which means he can't upload any more content for two weeks. If he gets a third strike within 90 days, he could be permanently banned.

Sinn said:

I record the events here in Seattle... and [my brother] records the events in California. We edit the videos when we can and upload them to my YouTube channel. I currently have 1600+ videos from Flea to Hobby Weight robots. I make no money from these videos, so these videos didn't hurt me monetarily, but some of the best bot designs were taken off—like Dark Pummeler and Launchpad McWhack. Now I have appealed all my videos. I have no plans on quitting in recording or competing.

Andrew Rossol had several videos removed that he shot at RoboGames2017. Rossol has been uploading videos on behalf of the BattleBots team Deep Six for more than 13 years. "I think it's crazy that this stuff gets flagged," he said.

Rossol's fight videos did include some bot names that might suggest animals, such as "Sliver King vs catKong - RoboGames 2017." But no actual animals are found in the video.

Henry Aird, another Seattle-area builder and competitor, also received takedown notices for videos from a Western Allied Robotics (WAR) event uploaded in May 2015. Unlike both Sinn and Rossol, his videos were not named in a way that might give any indication as to their content. They contained no "insect" tags, which puzzled Aird.

"The strange thing is my videos were named '0037' and '0050,'" Aird said. "I didn't change the video names or even tag them—they were just hastily uploaded to my page and sent to someone else to sort out, essentially. And they still got flagged for animal cruelty, so nothing makes any sense to me."

The takedown notices make clear that the videos had been "reviewed" by YouTube first. This raises questions about what these reviews look like. Is the "reviewer" a computer program? It seems unlikely that humans actually looked at the videos in question.

We asked YouTube what happened here, and a spokesperson told us that the site sometimes gets it wrong. "With the massive volume of videos on our site, sometimes we make the wrong call," said the spokesperson. "When it's brought to our attention that a video has been removed mistakenly, we act quickly to reinstate it. We also offer uploaders the ability to appeal removals, and we will re-review the content."

There is not, we were told, any prohibition on robot fighting videos.

After the issue was noticed, most (but not all) of the videos made a sudden, unannounced return early on August 20.

Moderation at scale is hard, and it's tempting to turn to algorithms, AI, and machine learning to help. But this story is a prime example of why human judgment remains a part of the digital systems that increasingly influence our lives.