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On Fire

What is this?

This project is a Discord bot developed for my local fantasy league (Omarball) to be used in the league's Discord server. It was inspired by r/fantasybball posts from u/nerdyog15 where each post would sum the best and worst lines of the day.

on fire updated example

What packages and APIs are used in this project?

I coded this in Python using the Ball Don't Lie API and ESPN API package. There is also an R script stored that holds all the calculations for z-scores; the script fetches all cumulative stats for players per season and then calculates the average stats for players who play 24 minutes or more on average per game during the season. The mean and SD values are taken from the script into the Python script to calculate the final Z-scores.

Note: The R script is not meant to be used when performing the actual On Fire script, but rather serves as a separate document that can be ran on its own to demonstrate the mathematical concepts and mean/SD values utilized in the final script. Make sure to download Tidyverse and hoopR if you would like to (mostly) replicate it.

How does the bot work?

This bot is given a unique channel in the Omarball server to post in. Every night at 11:30 PM PST (as generally all NBA games will be done for the day by this point), a BAT file I created is automatically run to activate the scraping and then the bot to post the list of best and worst lines.

The scraping aspect utilizes the ESPN API package to fetch rosters for each Omarball GM along with the name of the GM's team. Once player lines are obtained via Ball Don't Lie, the script maps GMs who own the respective players into the dataframe. After scraping is completed, z scores are calculated for each player line using mean and SD s obtained for the NBA categories on a season-wide basis. With the z-scores, two printouts are created: one is for the best lines with the BDL DF sorted by descending order in regard to the 'ZSUM' (or, sum of a player's z scores across all categories) and another is for the worst lines with the same DF sorted by ascending order. Once these printouts are created, the script moves into the Discord bot phase where it will make two separate posts, one for the best lines and another for the worst lines.

Note: How many lines the bot will post depends on the amount of lines available and, in turn, how many games were played for the day. If there are less than 30 lines available once unrostered players are dropped (and, for the worst lines, all players who played less than 24 min. are also dropped), the script will shorten the posts to provide only the best and worst 5 five lines. Otherwise, it will post the best and worst 10 lines.

What do the emoji and bold text mean?

Here's a quick legend for the emoji:

  • Bolded stats refer to a great counting stat that had a z score of 2.5 or above.
    • Note: "Counting" stats refer to categories where you win simply by having a higher amount of them for the week: these include more points, rebounds, assists, blocks, and steals.
  • 🤯 refers to a fantastic stat; players earn this emoji for a specific category if they have a Z score of 3.5 or above when it comes to counting stats (points, rebs, asts, blocks)
    • This also applies to steals, but here, the Z cutoff is about 8.4655 (or, four steals).
  • 🤮 refers to very high turnovers; the cutoff for this emoji is a Z score of -1.08151 (or, five turnovers minimum).
  • 🎯 refers to great accuracy relative to shooting volume; players earn this emoji if they have a Z score of 3.25 or above when it comes to volume stats (fg%, ft%)
  • 🧱 is vice versa and refers to awful accuracy relative to volume: players earn this emoji if they have a Z score of -3.25 or below for volume stats
  • 3️⃣🚀 means a player got a triple double!
    • A "triple double" (also known as triple dub informally) refers to when a player earns double-digit stats in at least three counting stat categories during a game. For example, if a player were to earn at least 10 points, 10 rebounds, and 10 assists, they would earn a triple double.

Note: You might notice that the turnover and steal criteria don't have the same Z cutoff compared to other categories like points and rebounds: admittedly in these cases these are arbitrarily decided cutoffs. With fantasy, I tried to choose cutoffs based on which kind of line would make a GM react strongly (positively or negatively), with five turnovers and four steals generally being the case. If you were to determine what was an "outlier" (or absolutely great/terrible value) in an actual study such as one for sports analytics and were specifically using Z scores, do not use arbitrary cut-offs.

Can players only get great emoji if they show up in the best lines list (and vice versa?)

No. The best and worst lines lists are sorted by an overall zsum, and all other stat calculations attached to the emoji (and bold text) are done on a per-category basis. This could mean that even if Giannis went 1/6 from the free throw line and got a "🧱" emoji due to awful accuracy, he could still have one of the best lines of the night due to his other categories by having plenty of points, rebounds and assists.

Why did you use ESPN API info?

There are two reasons as to why this bot does this, both ultimately in order to differentiate itself in purpose and functionality from Reddit posts with the best lines:

  1. Being able to hook ESPN API info allows the bot to comprehend who exactly is reaping the best lines of the day. For example, if we didn't have this info, the bot could still understand Steph having the best line of the night with a 50-bomb, but it's not going to know what GM is reaping Steph's 50-bomb. In other words, this can showcase which teams are dominating each day in terms of getting the best lines or also show when there's competitive nights between all GMs, ultimately adding a personal element of analysis relevant to the Omarball league.
  2. Part of the fun of fantasy is scouting in (relative) secrecy for FAs that are beginning to develop on the court and providing competitive lines. A functionality of this bot is being able to show only lines from those who are rostered in Omarball in order to retain a bit of this secrecy. If this bot showed all lines, we might run the risk of having all GMs in Omarball see great FA lines at the same time, which could then reduce the element of scouting into simply being the first to add a player once the nightly list post drops. The template of this function can help a bit with encouraging your GMs to conduct independent scouting and take an active role in looking for great players.

Why filter out players who played less than 14 min. for the worst lines printout?

The problematic aspect of not filtering out players with very low minutes is primarily in regard to how the Z score is calculated. There are two scenarios to consider:

  1. If a player is injured and did not play (or, in rarer cases for fantasy, got DNPed), the ESPN API which will fetch the roster is not able to automatically filter out players who played zero minutes for a specific game (as by and large, it does not get individual scores for a game but rather cumulative stats). This would mean that if the players who played zero minutes were included in the final printout, they're effectively considered some of the "worst" when z-s are calculated becase they have no stats in the first place. We need to filter out these players in this situation so we can understand which players truly disappointed in the fantasy^* spotlight.
  2. Even when not considering players who DNP in a game, there's other factors which make it risky to include players who played between 1-13 minutes. Injuries still remain key to consider: a player might get injured only a couple minutes after they start playing and then be forced to miss the game. 14 minutes as a cutoff allows us to avoid a decent amount of early injury situations while also allowing for players who simply got blown out and got little runtime before being pulled to still show up in the list. Note: Emphasis on fantasy in terms of "disappointing"! This is not a true metric to judge player quality in the NBA itself. See below for further info on why this should not be used to measure player rating.

Why not use the same filter on the best lines section for consistency?

I find this idea more subject to change (I welcome feedback here!), but my belief is that if there were a hypothetical situation where a player delivered amazing stats within little minutes, we should allow to show it when it occurs in the final printout. Of course, the concern is that this could mean that players with low minutes overall get their fantasy value inflated by too much due to low turnovers; this should be mitigated as we effectively "punt" it in our measurements by weighing it to -0.25. Meanwhile, for "worst" scores with low minutes, as aforementioned it will simply weigh injured players by too much unless they are filtered out early. In other words, if a player is on IR, they should not be expected to be defined as players to be judged based on their (non-existent) "performance."

I see constants added on top of most of the z-score category calculations, why is that?

I have applied weights to CATs that have high variance in order to mitigate inflated fantasy value produced by players having more blocks or steals than usual, slightly higher FG% per volume than the average, or having low turnovers when they didn't do much else in the first place due to limited minutes and/or a sidelined role. This is not to discount the fantasy value players can provide in these CATs: they are still considered valuable especially in situations where 1) stocks are rare to find in the first place or 2) just a tenth of an increase in FG% or one more turnover can make or break the week. However, this bot is attempting to highlight the best overall lines, and lines with even slightly higher than usual FG, stocks (blocks and steals) or zero turnovers can make it eligible for being one of the "best" lines even if the player's overall value wasn't that great for the GM (i.e. Holmes's line on March 20th 2024 would have been #10 on the list had we not weighed FG down). I consider this as another idea subject to change though; I welcome any suggestions on how to approach the weights, and of course you're also free to modify how you weigh these calculations in the actual script.

Will the mean and SDs used for the z-score calculations change in future NBA seasons?

Probably. Gilani's hoopR package is excellent and you would only need to modify certain arguments such as the year values are obtained from in order to generate new mean and SD values for each season. Ideally I would like to update the calculation values once a year around mid-March when the majority of the regular season is done and teams are beginning to fully tank or shut down players for off-season or pre-playoff rest.

With the mean and SD values for each category, could I use z scores to calculate the percentile of lines for the day relative to average player lines?

In most cases, no. The reason why is in regard to the nature of the distributions that you would obtain via the hoopR package (or whichever NBA API package you prefer in Python): much of the distributions, even if you were to control for players who played less than 24 minutes on average per game, are still heavily skewed. Although Z-scores can be calculated for any type of distribution, normal or not, you cannot interpret a percentile value from a Z value calculated for a skewed distribution. If you want to see exactly how these distributions are skewed, take a look at the plot grid of average NBA stats for 2023-24 below (among players with 24 or more minutes per game on average) and take note of certain categories like points and rebounds where they are positively skewed:

image

You might ask then why we don't use a transformation like log conversion to make this distribution normal and allow for percentile calculations. In this case, I would advise reading this comment thread from r/fantasybball that clarified some common misconceptions about how z-scores in fantasy basketball work. Of specific note is a comment here by u/zeros1123 in regard to documentation they wrote on the broader idea of z scores in fantasy and why, vice versa, we shouldn't try to convert the distributions and attempt to make them standard in this case:

I wrote the readme, and agree fully with your explanation for why people are getting confused here. The Z-score is only "valid" for calculating percentiles based on the standard normal table under the condition that data is normally distributed. However, that has no bearing for its use in other contexts. The argument I presented in the readme never assumes that the underlying data is normally distributed. In addition to being unnecessary, artificially transforming non-normal distributions into normal distributions can also cause problems. Scores should always be linearly additive, that is, two players who score two 3-pointers each should be exactly as valuable as one player who scores zero and one who scores four. If we warp the data to make it fit a normal distribution, that may no longer be true, which is clearly undesirable for a value-quantification system

Can I use this tool (and attached formulas) to gauge overall player value (non-fantasy) in the NBA?

This is something I would not advise doing. As much as it is fun to discuss the best and worst fantasy lines for the night, fantasy metrics are in the end overfocused on basic stats such as counting stats (i.e. points, rebounds) and do not account for impact in other means such as off-ball defense. Other advanced tools and metrics exist for measuring such variables and giving a better sense of how valuable an NBA player is. In general, do not try to take away any major ideas about how "good" an NBA player is in the league using Z-scores from this tool alone. This tool is meant for fantasy only and, in turn, should only be used as an informal means of calculating how well a player did for your fantasy team during a specific night.

Can I run this script for my league's server?

Sure! This bot doesn't have an OAuth invite link on hand given that it only uses API info for my league, but you can utilize the basic template, create your own Discord bot to host it and things should work the same. Things you would need to specifically do outside of using the basic script would mainly be in setting up a 'config.py' file which includes:

You would also need to download relevant Python packages via pip or otherwise, including:

  • Pandas
  • Discord.py
  • ESPN API

WARNING: IF you fork and/or host a version of this script on GitHub, DO NOT PLACE YOUR API KEYS AND TOKENS IN THE MAIN SCRIPT! Create a separate config file with the defined API keys included or a VENV file, mark the file to be ignored on commits with .gitignore (along with all PYC files), and DO NOT give out any of these keys.

In terms of the automation for posting it every night at 11:30 PM PST (or whichever time you prefer), if you just want to host it locally, you can utilize Windows Task Scheduler to do so. If you're specifically using an Anaconda environment to host the actual On Fire script, you would create a BAT file with this template after cloning the repo and doing the work in setting up the config:

call C:\Users\InsertUserNameHere\anaconda3\Scripts\activate.bat
call conda activate environment_name
call python C:\Users\InsertUserNameHere\InsertRepoParentFolderName\omarball-onfire-bot\on_fire.py
call conda deactivate
pause

This will run the script and keep the terminal open to assist in debugging when needed. When the BAT file is ready, point Task Scheduler to the BAT file and schedule it for the time you prefer.

Will you automate set-up for all leagues and create a invite link for the bot in the future?

It's a possibility, but more details and personal time are needed here before I can proceed. I would need to specifically consider if there are any potential security concerns with obtaining ESPN cookie and SWID info through user input (this would be through DM if I were to do so). If I pursue a version that can join any server and take in user's S2 and SWID to create the league connection, it would be through a branch of the original repo. For now, you are free to use the basic template of the script to host it on whichever server you desire.

Who do you want to thank?