"My rule was I wouldn't recruit a kid if he had grass in front of his house.
That's not my world. My world was a cracked sidewalk." —Al McGuire

Thursday, July 07, 2022

Who Will Score? Part V: Calculating eFG%

Graphic from fourpointplays.wordpress.com

For basketball stats nerds, Effective Field Goal Percentage is king. Offensive efficiency is measured with four factors. The original explanation from Dean Oliver, author of Basketball on Paper, is included in that link, but essentially eFG% tells you how many points a team or player scores per shot taken. It is by far the most important predictor when it comes to winning basketball. The more efficiently you shoot and the less efficiently your opponent shoots, the more you are likely to win. It is similar to typical field goal percentage except three point shots made get an extra 0.5 points per made shot to reflect that 3 is 50% more than 2.

Our predictions were based on returning player that had adequate stats and comparable players that allowed our projections with reasonable mathematical confidence. In short, it's easier to look at what Tyler Kolek did the past two years and compare that to other up-transfers that with similar paths than to project what Ben Gold will be with no idea how his NBADL experience will translate to the D1 level.

We focused on the six most prolific returning players, which led us to look back at the six players who played the most minutes last year. Here are the top-six in minutes, their makes by category, calculated eFG%, and cumulative eFG%:

2022 2PFGM 2022 3PFGM 2022 FGA eFG%
Justin Lewis 137 58 443 50.6
Tyler Kolek 36 36 225 40.0
Darryl Morsell 106 43 334 51.0
O-Max Prosper 57 19 165 51.8
Kur Kuath 82 0 115 71.3
Oso Ighodaro 73 0 108 67.6
Combined 491 156 1390 52.2

While this doesn't include prolific three-point shooters like Kam Jones and Greg Elliott, that 52.2% eFG% is very close to being in line with the team eFG% of 52.1% in 2021-22. As go the top players on the team in terms of minutes, so goes the team as a whole. That 52.1% eFG% ranked 77th overall and helped lead to an Adjusted Offensive Efficiency Rank of 66. So what does that have to do with next season?

David Joplin & Kam Jones putting in work
 Photo by Jovanny Hernandez | JS Online

Because we are projecting expected eFG% for the top-six returning players, we can line up those players against the players above. For further context, the above players accounted for 73.4% of minutes played last year. Using our 2022-23 projections, the top-six (Tyler Kolek, Kam Jones, O-Max Prosper, Oso Ighodaro, Stevie Mitchell, and David Joplin) would account for 69.1% of minutes. A little bit less, but close enough to be relevant for our purposes.

Using the following formula, we can estimate the number of shots each player will take per game:

60 x % Minutes x % Shots = ?

60 is the number of expected shots per game, and by calculating the percentage of minutes played and the percentage of shots taken when a player is on the court, it gives us an expected number of shots taken per game. Then by multiplying that by 32, which is the number of games Marquette played in 2021-22 and the number of games they would play in 2022-23 assuming all regular season games and one Big East Tournament game, we know the number of shots each player would take. By multiplying that total by the eFG%, we have a number of effective makes. It won't give us actual 2PFGM or 3PFGM, but for instance in 2021-22, Justin Lewis would have an effective make total of 224, taken from the eFG% numerator calculation. Divide that 224 into his 443 field goal attempts and you get 50.6%, matching his eFG%.

The same would apply to our 2022-23 projections, with the added bonus that by calculating the top-six players' effective makes, we can measure those against their expected field goal attempts and by adding it all together, come up with an expected eFG% for those six players, and by extension the entire team. Here are the numbers:

Eff. FGM 2022-23 FGA eFG%
Tyler Kolek 129.4 265.7 48.7
Kam Jones 173 302.5 57.2
O-Max Prosper 123.1 218.2 56.4
Oso Ighodaro 109.7 164.4 66.7
Stevie Mitchell 79.2 148.7 53.3
David Joplin 100.2 207.4 48.3
Combined 714.6 1306.9 54.7

To provide some context in terms of reliability, the minute tally above equates to 94.1% of the 2021-22 minutes and the field goal attempts equate to 94.0% of the 2021-22 attempts. So if 2022-23 team eFG% is in close alignment with the top players in terms of minutes the way the 2021-22 team was, this is a strong indicator of eFG% improvement.

If the players improve at a rate comparable to the average sample (which included both the worst case and best case, so about average development) we can expect a 2.5% increase in eFG% in 2022-23. This makes sense as the two players that took the highest percentage of shots both had eFG% ratings under the team 52.2% average. While Marquette will be losing points, there is reason to believe they will be increasing their offensive efficiency.

To put into context what that hypothetical 2.5% increase would mean, Marquette's 52.1% ranked 77th in eFG% in 2021-22 but if they increased their team eFG% to 54.7% they would've ranked 21st in the category. And while the overall offense finished 66th, in 2021-22 every high-major team that ranked in the top-30 of eFG% was ranked in the top-41 of overall Adjusted Offensive Efficiency. That would mean an minimum expected 25-spot jump for Marquette in Adjusted Offensive Efficiency.

While Marquette doesn't project to have the individual scoring leaders they had last year, they are in line to have more players capable of stepping up on any given night and a more diverse and efficient offense. So the answer to the question of "Who will score?" is "It doesn't matter, as long as it's more efficient."

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