Does Winning the First Quarter Really Matter in the NBA?

Set the tone. Get ahead early. Win each quarter.

Coaches -- well, at least the rec-level and high school coaches I've ever had -- love to hammer home the importance of getting early leads and winning each quarter. But the first quarter really isn't that crucial at the NBA level, right? I mean, Bryan Mears discovered NBA defenders are farther from shooters in the first quarter than in any other, which stands to reason. Amp up the defense late in the game if you need to, but don't overdo it early in the game so that you have the energy to step it up in the final few minutes.

But can teams really afford to wait that long to give it their all? Or does winning the first quarter really help teams win their games? (Or, more accurately, is there a correlation between first quarter point differential and winning percentage?)

Setting the Tone

First, I'll set the tone for what exactly I did. From and including Christmas Day 2014 up until and including January 16, 2015, 173 NBA games occurred. That means that, with two teams in each, 346 unique first quarters exist, naturally linked with a corresponding first quarter from the opponent.

Ideally, I could have pulled data from a larger sample, but it didn't seem necessary in this case. I used the Play Index from basketball-reference.com to grab the quarter splits for these 173 games.

Then, I did some simple calculations and found winning percentages for the teams who won a particular quarter.

Setting the Tone?

Now, we can ask the question of whether winning the first quarter matters. It appears to be so -- this year at least.

This table shows the total instances in which a team actually won the given quarter (i.e. didn't tie the other team in that quarter). It also shows how many times the winner of that quarter won the game or lost the game.

While the team that won the first quarter eventually won the game 68.26% of the time in this span, teams that won the third quarter actually won a higher percentage of the games. Overlap surely existed, and again, pooling from a larger group of games may have changed the numbers, but my main intention was to see whether winning the first quarter really mattered at all -- and it sure seems to matter -- especially more than the fourth quarter.

And when looking at the correlations between first quarter point differential and winning percentage, it's almost a sure thing, but this year isn't exactly like the others.

Winners Win the First Quarter

Through January 16, six teams had a first-quarter point differential at or greater than 2.0 points. They are, mostly, good teams.

That really shouldn't surprise anyone. Some of the best teams in the league go out and get leads on teams -- particularly bad ones. After all, the four teams with point differentials worse than -2.0 points in the first quarter are the Lakers (-2.4), Timberwolves (-3.6), Knicks (-3.9), and 76ers (-5.4).

But consistent with the fourth quarter splits in the previous section being lower than any other quarter (with fourth-quarter winners winning just 59.38% of games) and the not-so-great splits from the six winning teams in the above table, the correlation between point differential is significantly stronger in the first quarter than in any other. (Correlations range from -1 to 1, with 1 being an absolute correlation.)

So, there's a really strong correlation between winning the first quarter and being a winning team. Also, the fourth quarter point differentials don't really matter. That stands to reason -- good teams can let up late, and bad teams can rack up points and close the gap to no avail.

You can see a fuller breakdown in the chart below. Each point on the x-axis (winning percentage) will have two points (or more if teams have identical win percentages).

The lower left quadrant has a decent amount of blue squares. These are the bad teams in the first quarter (Lakers, T'Wolves, Knicks, Sixers).

While the blue tends up in a fairly straight, diagonal line (because the correlation is close to 1), the red diamonds are scattered pretty randomly. Still, it's not as though winning teams all have negative point differentials in the fourth. In fact, only two of the 15 teams with a positive fourth-quarter are below .500 (the Knicks and Pacers).

Not Necessarily Causation, But It's Noteworthy

I'm not trying to conclude that winning the first quarter causes the winning of games, but there is a very strong correlation between winning the first quarter and winning games over the course of the season.

In 2012-13, there really wasn't, and the first quarter differential had the weakest correlation of any quarter. In that season, though, there were only two instances of a team's having a differential greater than 3.0 points in a single quarter. Both were first quarters. The Oklahoma City Thunder, who had a 73.2% win percentage (second-best in the NBA), won the first quarter by an average of 3.4 points. The Charlotte Bobcats (24.4%, second-worst in the league) lost it by 3.3 points.

There's a big drop this year (evidenced by the weak teams in first quarter differential). And last season, it was more like this year, too, which is why the correlation suggests the first quarter was most important last year. The 76ers (-3.7) and Bucks (-3.9), the two worst teams in the league record-wise, had the only first quarter differential greater than 3.0 one way or another. Also, the Pacers (68.3% winners, fourth-best in the league) had a third-quarter differential of 3.4 last year, and the Lakers (32.9%, 25th) were at -3.0 and the 76ers were at -3.8.

Though it wasn't the case in 2012-13, teams with good first quarter splits have been quite successful. I'm not saying they won because they won the first quarter, but at least for the last two years, good teams have won the first quarter.