NBA draft lottery

Before 1985: Territorial picks and coin flip

In the earlier drafts, the teams would draft in reverse order of their win-loss record. However, a special territorial-pick rule allowed a team to draft a player from its local area. If a team decided to use its territorial pick, it forfeited its first-round pick in the draft. The territorial pick rules remained until the NBA revamped the draft system in 1966.

In 1966, the NBA introduced a coin flip between the worst teams in each division to determine who would obtain the first overall draft pick. The team who lost the coin flip would get the second pick, while the rest of the first-round picks were determined in reverse order of the win-loss record. In this system, the second-worst team would never have a chance to obtain the first pick if it was in the same division as the worst team. The coin flip meant that both teams had an equal chance to draft first. The coin-flip system remained in operation until 1984.

1985–1989: Early lottery system

After the 1984 coin flip, which was won by the Houston Rockets, the NBA introduced the lottery system to counter the accusations that the Rockets and several other teams were deliberately losing their regular season games in order to secure the worst record and consequently the chance to obtain the first pick. The lottery system involved a random drawing of an envelope from a hopper. Inside each of the envelopes was the non-playoff team names. The team whose envelope was drawn first would get the first pick. The process was then repeated until the rest of the lottery picks were determined. In this system, each non-playoff team had an equal chance to obtain the first pick. The rest of the first-round picks were determined in reverse order of the win-loss record.

Starting from 1987, the NBA modified the lottery system so that only the first three picks were determined by the lottery. After the three envelopes were drawn, the remaining non-playoff teams would select in reverse order of their win-loss record. This meant that the team with the worst record could receive no worse than the fourth selection, and the second-worst team could pick no lower than fifth, and so on.

The New York Knicks were the first winner of the lottery in 1985. They selected Georgetown University standout Patrick Ewing with their first overall pick. However, speculation arose that the NBA had rigged the lottery so that the Knicks would be assured to get the first pick. Even though the envelope system was highly criticized, it was used until 1989 before being replaced by the weighted lottery system in 1990.

1990–present: Weighted lottery system

In 1990, the NBA changed the format of the lottery to give the team with the worst record the best chance of landing the first pick. The worst non-playoff team that season would have 11 chances, out of 66, to obtain the first pick. The second worst would have 10 chances, and so on. Similarly to the previous system, the weighted lottery system was also used only to determine the first three picks, while the rest of the teams selected in reverse order of their win-loss records.

Despite the weighted odds, the Orlando Magic managed to win the lottery in 1993 with only one chance to obtain the first pick as it was the best non-playoff team in the previous season. In October of 1993, the NBA modified the lottery system to give the team with the worst record a higher chance to win the draft lottery and to decrease the better teams' chances to win. The new system increased the chances of the worst team obtaining the first pick in the draft from 16.7 percent to 25 percent, while decreasing the chances of the best non-playoff team from 1.5 percent to 0.5 percent.

In the new system, 14 numbered table tennis balls were used. Then, a four-number combination from the 14 balls were drawn to determine the lottery winner. Prior to the draft, the NBA assigns 1,000 possible combinations to the non-playoff teams. The process was then repeated to determine the second and third pick. The table below shows the lottery chances and the probabilities for each team to win the first pick in the weighted lottery system in 1993 and 1994 draft.

In 2016 Dikembe Mutombo made people question the draft's legitimacy when he prematurely tweeted a congratulatory message to the Philadelphia 76ers for receiving the first pick hours before the lottery was conducted. Philadelphia did indeed win the first overall pick. Further questions were raised a bit when the NBA Draft revealed that every spot remained exactly the same as it was before the event took place, which was the first occurrence in draft lottery history.

In 1995, the NBA had an agreement with the two expansion franchises, the Toronto Raptors and the Vancouver Grizzlies that neither team would be eligible to obtain the first overall pick in the 1996, 1997 and 1998 drafts. The Raptors won the 1996 lottery but were forced to settle for the second pick. Another combination was drawn and resulted in the Philadelphia 76ers getting the first pick. Two years later, the Grizzlies won the lottery and likewise had to pick second in the draft, while the L.A. Clippers obtained the first pick.

Process

The lottery is normally held during either the third or fourth week of May.

To determine the winner, fourteen ping pong balls numbered 1–14 are placed in a standard lottery machine and four balls are randomly selected from the lot. Just as in most traditional lotteries, the order in which the numbers are drawn is not important. That is, 1-2-3-4 is considered to be the same as 4-3-2-1. There are a total of 1,001 combinations (or 14! / (10! x 4!)). Of these combinations, one outcome is disregarded and the remaining outcomes are distributed among the 14 non-playoff NBA teams. The combination 11-12-13-14 (in any order that those numbers are drawn) is not assigned and is ignored if drawn; this has never occurred in practice.

In the event a lottery pick is traded to another team, the record of the original team (whose pick it was before the trade) still determines eligibility for the lottery, and assignment of chances.

Since 2005, with 30 NBA teams, 16 qualify for the playoffs and the remaining 14 teams enter in the draft lottery. These 14 teams are ranked in reverse order of their regular season record and are assigned the following number of chances

1. 250 combinations, 25.0% chance of receiving the #1 pick
2. 199 combinations, 19.9% chance
3. 156 combinations, 15.6% chance
4. 119 combinations, 11.9% chance
5. 88 combinations, 8.8% chance
6. 63 combinations, 6.3% chance
7. 43 combinations, 4.3% chance
8. 28 combinations, 2.8% chance
9. 17 combinations, 1.7% chance
10. 11 combinations, 1.1% chance
11. 8 combinations, 0.8% chance
12. 7 combinations, 0.7% chance
13. 6 combinations, 0.6% chance
14. 5 combinations, 0.5% chance

Here are the odds for each seed to get specific picks if there were no ties (rounded to 3 decimal places):

In the event that teams finish with the same record, each tied team receives the average of the total number of combinations for the positions that they occupy. In 2007, the Minnesota Timberwolves and the Portland Trail Blazers tied for the sixth worst record. The average of the 6th and 7th positions in the lottery was taken, resulting in each team getting 53 combinations (the average of 63 and 43). Should the average number not be an integer, a coin flip is then used to determine which team or teams receive the extra combination. The result of the coin flip is also used to determine who receives the earlier pick in the event that neither of the tied teams wins one of the first three picks via the lottery.

The lottery is conducted with witnesses (from the accounting firm Ernst & Young) verifying that all fourteen balls are represented once as they are placed in the lottery machine. The balls are placed in the machine for 20 seconds to randomize before the first ball is drawn. The remaining three balls are drawn at 10-second intervals. NBA officials determine which team holds the winning combination and that franchise is awarded the #1 overall draft pick. The four balls are returned to the machine and the process is repeated to determine the second and third picks. In the event that a combination belongs to a team that has already won its pick (or if the one unassigned combination comes up), the round is repeated until a unique winner is determined. When the first three teams have been determined, the remaining picks are given out based on regular season record with the worst teams getting the highest picks. This assures each team that it can drop no more than three spots from its projected draft position.

In a case where a lottery team trades its pick to a playoff team, the playoff team assumes the lottery team's position in all draft lottery situations, unless provisioned by the conditions of the trade.

In 2014, the NBA Board of Governors voted on a proposed reform to the lottery. If the proposed changes passed, the four worst teams in the league would have been given identical odds (around 11 percent) at winning the top pick. The fifth team would have a 10 percent chance and the odds would decrease for each team picking after. The proposed changes would take away the advantage of having the worst record in the league (currently the worst team is given a 25% chance at the pick), and would work to keep teams competitive throughout the entire season. The final vote was 17-13 in favor of the reform, but that was short of the required 23 votes needed to push the change through.

Lottery ceremony

The drawing of the ping-pong balls is conducted in private, though observed by independent auditors and representatives from each team. The results are subsequently presented in a short ceremony (typically broadcast prior to or during halftime of an NBA playoff game), in which the order of the lottery is announced in reverse order, from the fourteenth selection to the first. Representatives from each NBA franchise with a lottery pick are present at the lottery ceremony.

The decision of not showing the ping-pong balls live has fueled speculation that the NBA will occasionally fix the draft lottery if it can benefit the league. The speculation originated with the 1985 draft lottery that sent Patrick Ewing to New York, with the theory being that the NBA wanted to send the best player in the draft to New York to increase ratings in a large television market. At that time, the NBA used 7 envelopes in a tumbler representing the seven teams with the worst record. Some have speculated that the envelope containing the Knicks logo was refrigerated beforehand, enabling David Stern to recognize and select it. Another conspiracy theory suggests that one of the seven envelopes was thrown into the tumbler, causing one of the corners to fold. After the envelopes were mixed, Stern took a deep breath before reaching into the tumbler and picking the envelope with the folded corner. No one has ever explained why all the other teams would go along with the fix. Afterward, the Draft Lottery Format was changed to the current ping-pong ball lottery in a private room with team representatives. However, despite the lack of any evidence, conspiracy theories still persist regarding the annual outcome of the lottery.

Lottery winners

The largest upset in the lottery occurred in 1993 when the Magic won the lottery with just a 1.5% chance to win. The second largest upsets occurred in 2008 and 2014 when the Chicago Bulls and Cleveland Cavaliers both won their respective lotteries with just a 1.7% chance. In 1999, the Charlotte Hornets also overcame long odds in the draft lottery when they won the third pick despite having the best record among all non-playoff teams. The Hornets only a 1.83% chance of winning a top-three pick. Since the lottery was introduced in 1985, only 18 of 30 NBA teams have won the lottery. The Los Angeles Clippers have won five lotteries, although two of them were conveyed to other teams in trades prior to the lottery. The Orlando Magic and Cleveland Cavaliers are second with three lottery wins each. Since the weighted lottery system was introduced in 1990, only four teams with the worst record went on to win the lottery while only four teams with the second-worst record have won the lottery.