End-of-Half Strategy in the NFL

If it happens to the team you're rooting for, you're pissed. If it happens to the team you're rooting against, you get cocky. But no matter what side you've been on, you've seen it happen: the offense using the final seconds of the first half to take a knee or otherwise kill the clock rather than trying to score.

Recent years have seen NFL coaches improve vastly in terms of avoiding old habits of risk aversion, whether that comes down to being more willing to roll the dice on fourth downs or on two-point conversion attempts. But despite this overarching trend, we still regularly see coaches decline to take risks when the game clock approaches halftime. Often we hear the justification of keeping momentum, and often we hear the ridiculous notion of "well, the offensive team gets the ball to open the second half anyway," as if who receives that kickoff should make any impact on a team's goal to maximize its points during the first half. Observing this pattern leads to a natural question: should coaches be more aggressive with the ball in the final seconds of the first half?

To answer this, I started with all of the play-by-play data available via NFLScrapR for the past 11 completed seasons (2009 to 2019). I removed all timeouts, kickoffs, and PATs, and then isolated all plays to occur in the last two minutes of the first half. PATs are removed because before 2018, NFLScrapR had a data entry flaw in which all PATs following defensive touchdowns were omitted. Kickoffs were removed because a kickoff return touchdown does not at all reflect a coach's offensive decision-making, and therefore isn't relevant to our question.

From there, I grouped all plays by the drive on which they occurred, creating a new data frame called PointsScoredOnDriveTable, which includes 4,347 drives. This table includes core information about every offensive drive to start in the final two minutes of a first half, including points scored, time remaining at the start of the drive, how many timeouts the offensive team had at the start of the drive, starting field position, and more.

Summary of the project: in most instances, coaches are deciding to be too passive in late first-half scenarios when it would benefit the offense to stay on the field. However, when it comes to situations when there is only time for one play before halftime, coaches are actually extremely accurate in deciding when to take a shot at the end zone.

The Basics: Are Teams Wasting Opportunities When They Could be Scoring?

For brevity and common sense, we can limit the bulk of the project to drives that start in an offensive team's own territory. If you can't figure out that attempting to score is the proper move when your starting field position is at the 50-yard line or inward, your pure fundamental cowardice goes beyond anything this paper could address. Most NFL coaches agree with this stance; since 2009, there have only been three kneeldowns taken on non-scoring drives in the final two minutes of the first half at the 50-yard line or closer, and one was accidental.

One more key distinction before getting into the analysis: taking a knee isn't the only way for an offense to demonstrate no real intent of scoring. If the offense gets the ball at its own 25 with 40 seconds left and executes one or two run plays before the clock hits zero, everyone watching the game knows that the offense meant to run out the clock. Because of this, I created a new metric, called "Quit" -- any drive was labeled a "Quit" if it started in the offense's own territory in the final two minutes of the half and did not include any pass attempts, offensive timeouts, or offensive touchdowns. (This last modification was because of a Chris Johnson 76-yard touchdown run in 2010 on the opening play of a drive starting with 1:56 left; we can't necessarily say that the offense's goal was to run out the clock there.) It's not a perfect metric, but within reason, if the offense doesn't pass the ball or call timeout once in a two-minute drill situation, we can say there was no real intent of scoring. The numbers back this up; since 2009, there have only been three rushing touchdowns of 50-plus yards in the final two minutes of the first half. (The other two came on drives that also included passing plays, and therefore wouldn't be labeled as "Quits" anyway.)

With these disclaimers out of the way, we can start by looking at the most basic question of all: how often are coaches "quitting" in pre-halftime situations to begin with? I did make a linear model (which I can show to any true statistics nerds interested), but what's much easier to interpret are the following graphs, which display data from the past 11 years. Keep in mind that the "Starting Field Pos" refers to distance from the opposing end zone -- e.g., 90 on the graph means the offense's own 10-yard line.



Looking at four plots simultaneously can be a bit overwhelming. So, here is the same data, but without considering how many timeouts the offense had:



We can see that "quitting" on a drive is very uncommon in most areas of the field when more than 40 seconds are left on the clock. If we use the approximations that result from not considering timeouts, "Quits" occur more than half the time inside a team's own 20-yard line in the 21- to 40-second range, and inside a team's own 40-yard line with 20 or fewer seconds.

Are coaches leaving points on the board in these situations?

This means that when it comes to field position, coaches are being too passive; in other words, it's almost always a good idea to try to score when your field position is at your own 30-yard line or better, but coaches neglect to do so in some situations. However, the red triangles are also shorter in the bottom plot. This means that when it comes to time on the clock, coaches are actually being too aggressive. Coaches almost always try to score with more than one minute left on the clock regardless of field position, but this is an ill-advised move if the field position is particularly bad, e.g., inside the own 10-yard line.

To summarize, it is still true that coaches are slightly too passive on average -- though it's difficult to tell to the naked eye, there is indeed more blue space in the top set of plots than the bottom. But now we have a more nuanced view of the thought process; coaches overreact to seeing a lot of time left on the clock, while they don't react enough to the prospect of above-average starting field position.