Sports in the US are exempt from anti-monopoly regulations, so they don't resemble markets in the first place. Baseball could, theoretically, also be efficient

Sports in the US are exempt from anti-monopoly regulations, so they don't resemble markets in the first place. Baseball could, theoretically, also be efficient by allowing entrepreneurs to start a new team with new Moneyball-like principles or even deeper pockets. But to buy or start a new team, you need your competition (the other teams) to agree with your plan. That's not an open market even slightly.