Welcome back! I am excited to announce that VolleyBTN has launched a new feature: the VolleyBTN Match Win Probability Calculator! I don’t know how familiar you are with other sports like basketball and football, but ESPN has a win probability feature for those sports that anyone can access in order to see the odds of a team winning during the game. I have been very interested in basketball lately and have really enjoyed seeing the win probabilities change during a match, but then I thought to myself “why doesn’t this tool exist online for volleyball?”. And then I realized that I could just make it myself. So I did!
I gave it some thought and decided there were two feasible ways to go about this. The first way would draw on lots of point-by-point data from past games. You could look at the data and find out what percent of teams that are up, say 15-13 in a particular set go on to win the game. So you could put in any score and get the percent of teams from your dataset who won the match in that situation. The second way would be to simulate the probabilities of winning a game based on the game situation, your team’s expected sideout percentage, and your team’s expected serve win percentage. I’ve done both, but the tool I’m introducing today takes the second approach. (I’ll compare the data and analysis from the first approach to the simulation tool in a later post).
The VolleyBTN Match Win Probability Calculator can be found here. The interface looks like this:
Here’s how the tool works:
First, you choose whether you are playing best of three or best of five sets. Then, you input the match situation. You identify how many sets you have won and how many sets your opponent has won in the match so far. Then, you input the score of the current set under your team’s score and your opponent’s score. After that, you flag whether you are the serving team or not. Finally, you enter the expected probability of your team winning a point on serve and your team’s probability of winning a point on serve receive (you can use what your own team’s serve and sideout percentage usually is).
Once you do all that, if you click “Calculate Win Probabilities” the tool will run 1000 simulations of the remainder of the game and report the probability your team wins the current set, the probability of winning the match based on the information you provided, and the probability of winning or losing in different numbers of sets.
Let’s work through a couple examples. Imagine for the moment that you’re in the fifth set of a match, and your team is serving, but you’re down 12 to 14. Suppose your team generally sides out at 60%, and that you have a strong stretch of servers coming in and you expect to win 60% of your service points. In this situation, even if you expect to win 60% of your service points going forward, you have only a 25% chance of winning the match. If the score was 13-14, your probability of winning would be just over 40%. But if the score was 14-14, your team would be expected to win 70% of the time.
Let’s consider how the calculator might work for a situation earlier in a match. Suppose your team has won the first set of a five-set match, but you are down 0-7 in the second set. If you think that both teams are evenly matched and both will side out, on average, 60% for the rest of the match, your team still has an almost 10% chance of winning the current set! And you still are slightly favored to win the match (54%).
This calculator is also interesting because it highlights how even small improvements in a team’s performance can greatly affect its probability of winning when it is matched against a comparable team. If two teams playing each other win 40% of their service points, not surprisingly the probability of winning a five-set match is 50-50. However, if one of the two teams are expected to win 41% of their service points, their odds of winning the match increase to 55%. If that team’s side out percent also increases to 61%, the odds of winning the match increase from 55% to 60%. So getting just 1% better at both serve receive and service win percentage could increase your team’s chance of winning against a comparable team by 10%!
I hope you find this tool interesting and useful!
Notes:
- Photo Credit: Cal Poly Athletics
- I created the VolleyBTN Match Win Probability Calculator using RShiny, which means that unfortunately I can’t embed the tool on this website, but am instead hosting the tool on shinyapps.io.
- If you’re using the tool but are unfamiliar with side out percentages, collegiate women’s volleyball teams often have average side out percentages close to 60%, for men’s volleyball it is typically a bit higher (often closer to 70%). But it does vary a great deal by level. For example, at lower levels and younger ages, teams may actually win more on serve than serve receive–at least once they’ve learned to serve consistently over the net!