Use an inflated balloon rather than a real volleyball, since a balloon moves slowly enough to be safe indoors and gives everyone extra time to react and get into position. Mark a simple boundary with a string, a piece of tape on the floor, or a row of chairs to act as the net, since a low, soft barrier is enough to divide the space and prevents injuries that a real net's tension could cause. Set the rule that the balloon must not touch the ground, and count a point whenever it does, since this keeps everyone actively moving and gives the game a clear way to end each round. Clear the surrounding area of furniture, breakable objects, and drinks before starting, since players will be diving and reaching in unpredictable directions to keep the balloon up. Play with a slightly underinflated balloon rather than a fully taut one, since an underinflated balloon flies more predictably and pops less often when hit. Rotate players in and out if you have more than four or five per side, since too many people chasing one balloon in a small space leads to collisions rather than actual rallies.