ONE has a lot going for it as the Asian UFC and a rising contender to the UFC's monopoly as they pick up more and more former UFC fighters and some notable American fighters (like BJJ legend Gordon Ryan who just finished ADCC after beating his own teacher!). But there's some shady practices involved as well. Fight analyst Jack Slack has many times criticized some of ONE's questionable practices. Given, Jack is a self admitted negative nancy and in very much a glass-half-empty type of bloke but he's not exactly wrong. Off the top of my head:

  1. Closed door weigh-ins
    The good: weight cutting is restricted to hydration levels. This prevents fighters from doing mega weight cuts that both give them a size advantage and can really hurt their health. Fighters, including well respected ones like DJ (Demetrius "Mighty Mouse" Johnson) have said how they like it and how it makes things easier for them.
    The bad: oh oops, all weigh ins are closed to the public and we really have no idea if a fighter is actually weighing in at the required weight or not. The ****?!
  2. Questionable scoring
    Jack Slack talked about this a little bit in his most recent Fights Gone By Podcast. Fights are not judged by rounds like in the UFC, but by overall performance. If your opponent gets more hits on you in the first two rounds but you come out and beat them within an inch of their life in the third round and leave them in a pool of their own blood, then you will win the decision. The head scratcher is that there's no scoring announced. ONE does list the criteria they use to judge the fights, but no scores are announced. The UFC uses a 10 point must scoring system which, while flawed, you can at least tell how many rounds a fighter lost and judges score cards are released to the media after a fight.
  3. Employees that manage or train fighters
    This one I'm fuzzy on; Jack Slack has spoken on it in the past if you feel like digging it up. DJ's coach has business ties with ONE and this is why he doesn't corner DJ when he fights. Now, DJ is considered pound-for-pound one of the best fighters in the world and one would have to be an absolute fool to question his abilities (fast as hell, great fight IQ, superior wrestling. Video game moves that earned him submission of the year. He does it all) so he doesn't need an insider's helping hand to be successful in MMA, but it still is questionable.
  4. Questionable decisions affecting a fight after it happened
    Another thing I've heard from Jack Slack (I'm still new to ONE and don't watch it regularly unlike the UFC. It's also not nearly as popular in the US so news doesn't travel as fast). Supposedly there have been some questionable overturning of decisions after a fight to possibly protect their golden goose (the Lee family; Angela and Christian). Now, Angela Lee is currently on a 2-fight losing streak (her only two losses in her career), one to TKO and the other to an IMO bad judge's decision and there has been no overturning so who knows I guess?
  5. No drug testing
    Because: "lolz no real martial artist are too honorable to do that so why would we?"
  6. Questions on longevity
    This may be why there's so much fuzzy stuff going on with ONE. Right now they're being funded by venture capital and are not making money yet. They're basically doing the Microsoft Xbox thing where they just keep failing and losing money until they iron out all their issues and takeover Asia (which they pretty much have I think. Other than ONE, the other two big promotions are Rizin and Jewels which aren't as big as ONE.