For rookie contracts, which salary increase is capped by the 25% rule?

The annual salary increase for rookie contracts is capped by the 25% rule, which is designed to maintain competitive balance within the league and control team payrolls. This rule states that a player's base salary cannot increase by more than 25% from one year to the next in the first four years of a rookie contract. This mechanism ensures that while players can earn more as they develop and prove themselves, the increases remain manageable for teams to budget effectively.

The other options pertain to different aspects of contracts. Signing bonus proration is often calculated differently and does not fall under the same increase restrictions. Workout bonuses are additional incentives that could vary significantly and aren’t directly tied to the capped salary increases. Base salary only refers to a component of the contract but doesn't fully capture the overall framework of restrictions that apply to the annual salary increase during a rookie contract. Thus, the focus remains on the structure of the increases, which is precisely what the 25% rule governs.