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Chance of Winning an NBA Series if you Win Game X

Fri Sep 11 2020

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    • I watch a lot of playoff basketball. I watch the pregame. I watch the postgame. I follow along on Twitter. I watch the highlights. I read the discussions. I laugh at memes. I look longingly at the Inside the NBA studio here in Atlanta on my morning commute. I say "Rings, Chuck" whenever someone questions anything I do. The whole 9 yards.

    Through all of that, there's really only one thing that bothers me. It's when Chris Weber/Doris/Stan/etc. (no one is innocent) chimes in with a fact from the math nerds saying (and I'm paraphrasing)

    "This is a huge game for them tonight. Historically, the team that wins game Y wins the series X% of the time."

    Every. Time.

    I can't help but think, "No way! The team that wins a game in a playoff series has a high chance of winning the series?" 😐

    So I had to crunch the numbers to answer the eternal question...

    What is the probability of winning the series if you win game X?

    Here are the results.

    Won game 1? 78.032% chance to win series
Won game 2? 70.684% chance to win series
Won game 3? 63.758% chance to win series
Won game 4? 63.912% chance to win series
Won game 5? 75.571% chance to win series
Won game 6? 70.588% chance to win series
Won game 7? 100.000% chance to win series

    NBA Win Prob

    There you go. Confirmed. The team that wins any game in the series has a very high probability to win the series.

    Here's the code. It was big time ugly, but I cleaned it up and it's not so awful. Normalize just hacking around. It's OK.

    PS

    So while I did spend the whole post claiming (tongue in cheek) that this is the least surprising and least interesting fact that gets regurgitated every broadcast, there are a few interesting bits here... as much as it pains me to say it.

    The first is the dip at game 6. What explains that? Are teams on the brink of losing in game 6 fighting with everything they've got while the team leading 3-2 is comfortable to coast?

    No. It's much less interesting.

    What's really happening is some playoff series used to be only best of 3, so 5 games total. That meant the team that won game 5 was the winner of the series. This 100% win rate brings up the chance in game 5.

    And that's all I can glean. When you distill data down like this you lose a lot of fidelity.

    But what I can say, only now that I have crunched all the numbers, is that the Celtics won game 7 against the Raptors, so statistically, they should have a 100% chance of winning the series.