Mystikal took a terrible fall during a concert Thursday night in Tampa ... it was so bad his concert got cut short by more than half and he couldn't walk off the stage without a major assist.
The rapper ran onstage at around 1 AM and within 30 seconds just at it ... he tumbled offstage to the floor below. Security helped him back up, but he was clearly injured and in pain.
He spent the next 45 minutes grimacing in pain as he sat on the edge of the stage ... unable to stand. At times he scooted a few feet, but that was it.
A concertgoer tells us, it was obvious to all something was seriously wrong, as Mystikal repeatedly said, "Man, I need an ambulance."
He finally pulled the plug as members of his crew helped him offstage without putting weight on the injured leg.
It's unclear if he went to the hospital.
As for what caused the fall, the eyewitness tells us a drink fell before he got onstage and it splashed all over the stage.