Scoring Drives – First Down Analysis

Overview

This post will look at how first downs affect scoring statistically.  Every first down converted by the offense leads to a higher likelihood of scoring points.  Ask yourself this:  How many first downs does it typically take to put a team in scoring position?  This post will hope to clear the picture on how each successive first down gets the team closer to scoring.

The Data

I have compiled three season’s worth of data for USC’s football team.  Specifically, I looked at the 2008, 2009, and 2010 football seasons.  Overall, there were 448 drives which were recorded and went into the analysis.  Drives which ended either the half or ended the game were not counted unless they resulted in a score.  This was due to the arbitrary nature of whether a drive was a “successful” drive in these situations.

Field goals were counted any time a field goal was attempted, regardless if the field goal was made or missed.  This analysis looks at the relationship between first downs and the offense getting into scoring position, so whether or not the field goal was made is generally irrelevant.  Also note that a field goal attempt will count whether it is a 50 yard attempt or a 20 yard attempt.

In this particular analysis, scoring the touchdown does not count as a first down conversion.  In my other analysis pieces, touchdowns are typically counted as conversions since the offense has converted on the required yardage.  However, to keep this data consistent, touchdowns were not counted as conversions here.

Scoring in Relation to First Downs

First, let us look at USC’s distribution of drives in terms of scoring.

The majority of drives ended without the team entering a scoring position.  56% of drives end unsuccessfully (a punt, failed 4th down conversion, or turnover).  10.3% of drives ended in a field goal attempt and 33.7% of drives ended in a touchdown.  A total of 44% of total drives ended in a scoring opportunity.

Now let us look at how first downs relate to any type of scoring attempt.  This includes drives ended in field goal attempts and drives ending in touchdowns.


Surprisingly enough, a team that converts at least two first downs is more likely to attempt a score than not.  With two first downs, USC had 34 drives end unsuccessfully but 52 drives ending in either a field goal attempt or touchdown.  Reaching four first down makes it overwhelmingly likely to end with a scoring attempt.  Five or more first downs essentially guarantees a scoring opportunity, although it should be noted that there was only a sample size of 11 drives with five or more first downs in three seasons.

Now let us take a closer look into these drives.  This next graph will differentiate between unsuccessful drives (no scoring opportunity), field goal attempts, and touchdown drives.  This first graph will look at the number of drives in each category, then we will look at the percentages.

Each first down drastically cuts down the amount of unsuccessful drives while increasing various scoring.  The graph tapers off near the end as there are fewer and fewer drives that reach that number of first downs.   Lets look at the same data, but reorganize it so that it is looking at the percentage chance for each outcome rather than the raw number of drives.

Just as in the original scoring graph, the key change is at two first downs.  At this point, it even becomes slightly more likely to score a touchdown (46.5%) compared to not getting any points at all (39.5%).  Also keep in mind the 14% chance of a field goal attempt after two first downs, which adds to the overall scoring opportunities when reaching at least two first downs.  Looking at the percentages shows the trends on how first downs affect various scoring.

Conclusion

First downs play an important role in football as they keep drives alive.  USC’s average drive converted 1.6 first downs.  However, the data suggests that even converting two first downs will make it more likely to attempt a score than not.  This was surprising to me, as I originally expected the tipping point to be between three and four first downs.  Up next will be an analysis on yards gained per drive.

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One response to “Scoring Drives – First Down Analysis

  1. Pingback: Yards per Scoring Drive Analysis « Trojan Football Statistics

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