Can you fight professionally (MMA BOXING) and sign contracts with organizations while serving active army?

Start with your local fight house first. You’re putting the cart before the horse. Unless you’re kicking everyone’s ass at your base fight house, it’s not something you have to worry about. Also, the Army has fight teams

Remember the CoC will have to approve any and all moonlighting!

If you're good enough you can. The last SEAC had one of his staff fighting for one of the lower tiered MMA organizations. But as with every other job, you have to get your CoC's OK.

As someone else suggested, check with your chain of command first. I was injured while working a part-time job as a mall security guard and my battalion commander told me that he was thinking about making me quit it. He didn't, but I had to promise to use more care. If you are injured during a match or training then your unit is negatively affected by it.

main sports in the United States.