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The NBA Draft Lottery, explained

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How the lottery works and what it means for the Dallas Mavericks.

2017 NBA Draft Photo by Mike Stobe/Getty Images

For the second time in as many years, the Dallas Mavericks ended the season as one of 14 lottery teams. But the lottery rules can feel opaque to fans of a team that’s not accustomed to losing. Here’s how it all works and what it means for the Mavericks.

How does the selection process work?

If you’ve been following the NBA for a long time, you probably have at least a vague ping-pong ball-filled notion of how the draft lottery works. But let’s break it down in a bit more detail.

The lottery machine is filled with 14 ping-pong balls numbered 1-14. The balls are drawn one at a time until a four-ball combination is formed. The order of the balls isn’t important, so (for example) a drawing of 1-8-13-9 is considered the same as 13-8-1-9.

The 14 ping-pong balls yield 1,001* possible four-ball combinations, but one (11-12-13-14) is discarded. The 1,000 remaining combinations are assigned to the 14 worst teams in the league, with the team with the worst record receiving the most and the team with the 14th worst record getting the fewest.

The lottery only determines the top three draft picks; after that, the order is determined solely by rank.

What happens when teams are tied?

When teams are tied, they each receive the average number of combinations for the two seeds. For example, Dallas was tied with the Atlanta Hawks for the third-worst record in the draft. So, they should have each received the average of 156 (the number of combinations assigned to the third-worst team) and 119 (the number received by the fourth-worst team).

But in this situation, that came out to 137.5. Because the ping-pong ball system only works with round numbers, there was a tie-breaker coin toss held yesterday to determine who got the extra pick, with the winner receiving 138 and the loser receiving 137 combinations.

The Mavericks came out on top in that coin toss, so they’ll be picking as the third seed.

What does that mean for Dallas?

So how does this play in terms of odds? Here’s a chart that shows how likely each seed is to receive each draft pick:

Odds of receiving draft picks by seed

Pick 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 13th 14th
Pick 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 13th 14th
Seed
1 25.0% 21.5% 17.8% 35.7%
2 19.9% 18.8% 17.1% 31.9% 12.3%
3 15.6% 15.7% 15.6% 22.6% 26.5% 4.0%
4 11.9% 12.6% 13.3% 9.9% 35.1% 16.0% 1.2%
5 8.8% 9.7% 10.7% 26.1% 36.0% 8.4% 0.4%
6 6.3% 7.1% 8.1% 43.9% 30.5% 4.0% 0.1%
7 4.3% 4.9% 5.8% 59.9% 23.2% 1.8% 0.0%
8 2.8% 3.3% 3.9% 72.4% 16.8% 0.8% 0.0%
9 1.7% 2.0% 2.4% 81.3% 12.2% 0.4% 0.0%
10 1.1% 1.3% 1.6% 87.0% 8.9% 0.2% 0.0%
11 0.8% 0.9% 1.2% 90.7% 6.3% 0.1% 0.0%
12 0.7% 0.8% 1.0% 93.5% 3.9% 0.0%
13 0.6% 0.7% 0.9% 96.0% 1.8%
14 0.5% 0.6% 0.7% 98.2%

Because of the tie, Dallas’ odds of receiving the No. 1 pick are 13.8 percent (they would have been 13.7 percent if they’d lost the coin toss, so not a huge change). Winning the tie breaker is a much bigger deal, though, when it comes to the team’s floor. The Mavericks have a roughly 42.4 percent chance of a top-three pick and a nearly 90 percent shot at a top-five pick. And because only the top-three picks are assigned by lottery, the Mavericks can’t drop any lower than sixth in the draft. If they’d lost the coin toss, they’d have only been guaranteed a top-seven pick.

Crazy things have certainly happened on lottery night, though. In 1993, the Orlando Magic won the lottery after finishing the season with the 11th worst record and barely over 1.5 percent of the ping-pong ball combinations (the pick conveyed to Golden State, who drafted Chris Webber). More recently, the Cleveland Cavaliers took Andrew Wiggins first after ending the season ninth from the bottom.

What about lottery reform?

You may remember a lot of talk about anti-tanking reforms (in part because Mark Cuban was one of the leaders of the anti-tank crusade). In September of 2017, the NBA Board of Governors approved changes to the lottery that are intended to decrease the incentives to tank. But, these reforms don’t take effect until next season.

Starting in 2019, the three worst teams will share equal odds of acquiring the No. 1 pick, and the lottery will determine the top four picks of the draft rather than the top three. You can read more about those changes here.

*In case you’re curious, you get this number by dividing 14! by (10! x 4!), where 14 is the number of ping-pong balls, four is the number of ping-pong balls PER combination, and 10 is the difference between the two.