And nobody is calling this kind of "front running" illegal.

> like "murder, but without the killing someone", or "fraud, but without the deception".

In a murder analogy, you'd keep the killing but change something else, maybe it's properly manslaughter but people will still call you a murderer.

For "fraud without deception", let's look at what that entails. You lie. The victim knows you're lying, no deception involved, but they rely on your word. The victim is harmed. I think that's close enough to allow people to call it fraud, even if legally it's slightly different.

> "reacting to the public actions of other market participants"

The reason people dislike it is because it's not just 'reacting'. They're getting in their own action before the thing they're reacting to has finished.

> why don't you define it

Darawk defined this version for us. "front-running. Which is me seeing your order on exchange A and buying ahead of you on exchange B before your order arrives."