OP’s boxing example was a perfect illustration of the common use of the word rigged. It’s rigged because the outcome was predetermined but not presented that way to the outside viewer.
But it's still legal, no? That's my point. I'm not saying it's good, just that it's an entirely different beast from illegal conduct. US elections have always been rigged (see: legally required electoral college) but they've never been "stolen"/"illegitimate" AFAIK.
No. It’s illegal to fix a sanctioned boxing match. Both in the sense of being against the rules of the entity putting on the match, and in the sense of violating the law.
Wrestling is a different beast but boxing is heavily regulated in the US
You can rig a game of monopoly, you can rig a jury. The act of something being rigged is separate from it being legal. Sometimes it is both, sometimes it is not.
