The most boring heatmap

With the NBA season about to resume there has been a lot of talk of "rust". That with the long break and short lead-up teams will be sloppier than normal. They'll turn the ball over more. Not pass as much. Take easier shots (more 3 pointers rather than driving to the hoop etc.).

It's a conversation had at the beginning of every season. And one I've always wanted to nail down. I believe its a phenomena. But are we all being fooled? Is this just survivorship bias? After all, we don't talk about it when the team don't play sloppy.

I decided to scrape the team box score for every Boston Celtics game going back to 1946. That's some 6,000 games. And, I can't really find it.

The median turnovers per game, for instance, is about 16 per game over 70-odd seasons. The standard deviation is roughly one. Given this, over 70-odd seasons, six of the first ten games of the seasons are within one standard deviation in terms of turnovers per game.

That's 60% of the initial games within one standard deviation, which is roughly what you'd expect. Over seventy seasons there's little difference if you compare all the first games and all the last games.

I wanted to make a heatmap to visualise this. I grouped all the games (so, all the 1st games of the season are together, as are all the 10th games etc.) I did this for five basic game stats - turnovers, assists, 3 point percentage, field goal percentage and three point attempts.

Just for easy comparison I've normalised everything to a range from 0 to 1.

You can see roughly what I found with turnovers. Some spikes here and there. Field goal percentage appears to get somewhat better as the season progresses. But it's mostly uniform.

You may be able to make a better case for some other, advanced stats. Like true shooting percentage and effective field goal percentage. But my data on the advanced metrics was a little iffy so I decided to put it aside.

I'm still not entirely sold this isn't a phenomena. It just makes too much sense not to be true. So I'm not gonna call it yet. One theory may be that individual players have a greater variance than the team itself, especially over a long period. This would explain the heavy focus by commentators, as starters and stars draw outside attention.

So I might scrape the players box score next. But if anyone can point me at someone else taking a deep dive it would be appreciated.