Complex sentence: Several sports leagues have implemented salary caps, both as a method of keeping overall costs down, and to ensure parity between teams so wealthy teams cannot entrench dominance by signing many more top players than their rivals.
Split into simpler sentences: Several sports leagues have implemented salary caps, both as a method of keeping overall costs down, and to ensure parity between teams. This result being that wealthy teams cannot entrench dominance by signing many more top players than their rivals.