It doesn’t take everyone getting involved to call a game rigged.

Just paying or instructing the ref alone can already change the outcome of a game.

For example, if the league, together with the bookies, wants the game to go over,  let’s say in basketball the line is 240 points (which is pretty high and might push most bettors to take the under) .. the fix could be done through the refs. They’d just keep calling fouls, even for the smallest contact, so players keep going to the free-throw line. That alone can push the score higher.

Now, take the point spread. Let’s say one team is favored by -15.5, which is already a big number, so the public might bet on the other side. If the fix is in, refs can call fouls in favor of the favorites to make sure it ends in a blowout, easily covering that big spread.

Of course, this isn’t a 100% guarantee of the outcome, but most of the time, it result in their favor. And the thing is, they only need the ref to pull it off, sometimes the players themselves aren’t even aware. That’s why you’ll see players complaining about missed calls or questionable fouls.