Yes, umm.. Hello there. I've been playing this game for a couple of days and I've taken an interesting in sparring. I try to spar with other people, but.. My moves are stiff and have no flow. I watched some replays and wonder how do they fight so smooth with no stiffness and how they jump and it looks realistic.. Can you guys help?

first one is do not use youtube run!when extending a back knee hold the front knee to do an epic spin and kick him in the face.when jumping do that.when punching hold elbow for about 20 frames until the hand is REAAALY close,there you extend elbow.if he flies back try to do a backflip or relax all and lie there for a bit and use hold to get up.while dodging,extend neck and hold hips and knees.then its your choce to extend both hips and relax or extend knees.after that jump up and kick him in the back.if you lose balance while running just do a wushu opener that sets one foor back and the other foot in front.then jump up and do a double kick.if running,hold elbows use shoulders and pecs for a realistic jog.if you fall,try using lumbar or chest.

It basically consists in a lot of practice, Alkramoz.
My advice would be to play around frequently in Free Play, using 0 0 -30 gravity (it's the one that's commonly used for realistic purposes as opposed to 0 0 -9.82), at least a bit everyday.

Realism (and consequently sparring) usually comes later in. Starting to go that way on your first month of playing might be too rushed, but if you're persistent enough, go ahead and have fun. Just remember that we all failed a lot in order to become better.