Non-simultaneous trades in basketball

One of the pleasures of market design--a pleasure it shares with good gossip--is being able to explore in detail the rules by which other people live. The NBA Salary Cap FAQ is full of such details.

It turns out that some details involved in managing an NBA team have something in common with the non simultaneous kidney exchange chains I recently blogged about. This is because NBA teams can exchange players, but the Salary Cap imposes some constraints:

What are the rules regarding trades?
"Teams under the salary cap may make trades as they please, as long as they don't end up more than $100,000 above the salary cap following a trade. But if a team is over the cap, or they are under the cap and a trade would take them more than $100,000 over the cap, then an exception is required. An exception is the mechanism that allows a team to make trades or sign free agents and be over the salary cap. Since teams are usually over the salary cap, trades are usually accomplished using exceptions."

What is the Traded Player exception?
"The Traded Player exception is the primary means used by teams over the cap for completing trades. It allows teams to make trades that leave them over the cap, but it places several restrictions on those trades. Trades using the Traded Player exception are classified into two categories: simultaneous and non-simultaneous. As its name suggests, a simultaneous trade takes place all at once. Teams can acquire up to 125% plus $100,000 of the salaries they are trading in a simultaneous trade. For example, a team trading a $5 million player in a simultaneous trade can receive one or more players whose salary is no more than 125% of $5 million, plus $100,000, or $6.35 million in return.
A non-simultaneous trade may take up to a year to complete. "

What is a non-simultaneous trade?
"A trade in which more than one player is traded away can only be simultaneous; non-simultaneous trades are allowed only when a single player is traded away (although teams can sometimes find ways to configure multi-player trades as multiple single-player trades which are non-simultaneous).
Here is an example of a non-simultaneous trade: a team trades away a $2 million player for a $1 million player. Sometime in the next year, they trade a draft pick (with zero trade value itself) for a $1.1 million player to complete the earlier trade. They ended up acquiring $2.1 million in salary for their $2 million player -- they just didn't do it all at once, or even necessarily with the same trading partner.
In the above example, after the initial trade of the $2 million player for the $1 million player, it was like the team had a "credit" for one year, with which they could acquire up to $1.1 million in salaries without having to send out salaries to match. ....
"Here is a more complicated example of a legal non-simultaneous trade: a team has a $4 million Traded Player exception from an earlier trade, and a $10 million player it currently wants to trade. Another team has three players making $4 million, $5 million and $7 million, and the teams want to do a three-for-one trade with these players. This is legal -- the $5 million and $7 million players together make less than the 125% plus $100,000 allowed for the $10 million player ($12,600,000), and the $4 million player exactly fits within the $4 million Traded Player exception. So the $4 million player actually completes the previous trade, leaving the two teams trading a $10 million player for a $5 million and a $7 million player. From the other team's perspective it's all just one big simultaneous trade: their $4 million, $5 million and $7 million players for the $10 million player. "

HT Steve Leider (who we're trading, non-simultaneously, to Michigan next year)