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A large factor that may cause a lockout is 57 percent take-in players get from basketball-related income, or BRI.
If player salaries come in below 57 percent of BRI, the owners write checks to the players out of an escrow fund accumulated through payroll deductions. If at any point salaries are more than 57 percent, the players have to write checks to the owners.
An escrow fund, according to Wikipedia, is an arrangement where an independent trusted third-party receives and disburses money and/or documents for two or more transacting parties, with the timing of such disbursement by the third-party dependent on the performance by the parties of agreed-upon contractual provisions. The parties are the NBA owners and NBA Players' Association.
In short, the players want to keep the BRI because they allege salaries have dropped the past three years. However, despite any drop, players are still seeing their 57 percent no matter how much money is spent on salaries.
If the BRI is eliminated, owners would get a little more control over their books, and could, in essence, spend more without worrying about giving away money in any situation.