Bring a large pot of salted water to a boil. Cook the rotini pasta according to package directions until al dente. Drain and rinse under cold water to cool.
While the pasta cooks, pour the balsamic vinegar into a small saucepan. Simmer over medium heat for 8 to 10 minutes until it reduces by half and thickens slightly. Remove from heat and let it cool.
In a large mixing bowl, combine the cooled pasta, halved cherry tomatoes, mozzarella balls, torn basil, olive oil, salt, and black pepper. Toss gently to mix.
Drizzle the cooled balsamic reduction over the salad and toss once more to coat evenly. Serve at room temperature.