## Maybe "Hidden Yardage" Should Be More Hidden

The stats evolution in football has provided us with some exceptionally useful metrics (h/t to Bill, Brian, and everyone else), but there's one stat I've been seeing lately that's bothered me, namely "hidden yardage". Let me be clear, I think the concept behind it is useful, but I also think it can be a misleading stat. Let's look a little deeper.

The goal of hidden yardage is simple - not all drives begin at the same place, so looking only at offensive/defensive yards, number of scoring opportunities created, etc. doesn't provide the whole picture; however, if we calculate the average starting field position of each team, we can find the difference and multiply it by the number of possessions in the game to get an idea of how many yards were inadvertently generated by field position. A quick example can illustrate this concept:

If Team A continually has better field position that Team B, it will have fewer yards to go to score and so might end up with fewer yards, but more points. Let's look at FIU v. Charlotte from this last weekend for an example.

FIU had the following drives (starting field position, yards gained, result):

• FIU 25 - 67 yards - FG
• FIU 17 - 72 yards - FG
• FIU 25 - 33 yards - Punt
• FIU 45 - 55 yards - TD
• FIU 37 - 17 yards - Punt
• FIU 21 - 79 yards - TD
• FIU 25 - 18 yards - Punt
• FIU 25 - 75 yards - TD
• FIU 25 - 75 yards - TD
• CHAR 34 - 4 yards - Punt
Charlotte had the following drives (again, starting field position, yards gained, result):
• CHAR 25 - 75 yards - TD
• CHAR 25 - 36 yards - Fumble Return for TD
• CHAR 8 - 75 yards - Turnover on Downs
• CHAR 25 - 75 yards - TD
• CHAR 10 - 5 yards - Punt
• CHAR 25 - 1 yard - Punt
• CHAR 16 - 24 yards - End of Half
• CHAR 24 - 7 yards - Punt
• CHAR 10 - 90 yards - TD
• CHAR 25 - 75 yards - TD
• CHAR 25 - 75 yards - TD
• CHAR 2 - 11 yards - INT
Overall, FIU had an average starting field position of 31.1 with 490 yards gained and Charlotte an average starting field position of 18.3 with 534 yards gained (differences in yards gained from drives above due to penalties).

Now, obviously some of those drives are tricky (end of half, end of regulation), but we see that Charlotte gained 44 more total yards while having to overcome 12.8 more yards per drive. That might not seem like a lot, but over FIU's 10 possessions, we might look at that as an extra 128 yards that FIU did not have to gain up on offense. FIU only won by 7, so this probably had an effect, especially if we notice that early on FIU took over at their own 45 and only had to drive 55 yards to score whereas Charlotte had 4 drives start at or inside their own 10.

There are certainly better games to illustrate this point - I picked a random game from this week with a decent difference in starting field position and for which the losing team had more yards, but the main benefit of "hidden yards" is that it helps to quantify the effect of things like turnovers and good special teams play.

But there are other games in which "hidden yards" is deceiving. Let's take Penn State v. Rutgers for example. This game saw a 18.2 difference in field position in favor of Penn State. Extrapolated over 12.5 drives, that comes out to 227.5 "hidden yards"! Think that might have helped in a 13 point win? Probably, but maybe not as much as we'd think. Early in the game, we saw these drives:

• Rutgers started at its own 22, gained 8 yards, and punted 42 yards
• Penn State started at its own 28, gained 5 yards and punted 47 yards (because of a touchback)
• Rutgers started at its own 20, lost 10 yards, and punted for 39 yards
• Penn State started at the Rutgers 49, gained 6 yards, and punted 23 yards (because of a touchback)
• Rutgers started at its own 20, gained 5 yards, and punted 50 yards
• Penn State started at its own 25, gained 71 yards, and kicked a FG
What an ugly beginning to this game (I'm glad I missed it!). Ignoring the decision to kick the FG from the 4 yard line, we might be tempted to delve into the "hidden yardage" here and attribute Penn State's success to it. In these three drives for each team, Rutgers had an average starting field position of 20.7 and Penn State had an average starting field position of 34.7. That's a difference of 14! Over 3 drives, that's 42 hidden yards, which surely benefited Penn State, right? These hidden yards, one would think, would evidence turnovers or excellent special teams play, but neither of those happened. (Note that the ESPN box score was a little wonky, so that's why the numbers don't exactly match up. Either way, I think this proves the point.)

What actually happened here was that the field position battle had nothing to do with Penn State's eventual success that resulted in a field goal. Instead, we ended up in one of the scenarios in which hidden yards is misleading. Neither team gained more than 10 yards on their possessions here until Penn State drove the field 71 yards down almost to the Rutgers goal line, and Penn State actually began that drive at their own 25, so they didn't benefit from excellent field position. Most importantly, Rutgers arguably had the better special teams play (albeit due to two touchbacks), averaging 43.7 yards per punt to Penn State's 35 yards per punt in that sequence.

So what caused the "hidden yards" to be a misleading stat here? The answer is the punt sequence. There are probably much better examples of games in which this has happened than this one, but the basic concept is that punting back and forth with an equal amount of offensive success and special teams success really doesn't change much. Each drive may seem to have "hidden yardage" because of the better field position, but if the team with that "advantage" doesn't capitalize on it, did that yardage really occur?

Let's provide one more example, but we will use an extreme, hypothetical one, since that's usually an easy way to make a point. Let's say we have the following sequence:

• Team A starts on its 1 yard line, gains 0 yards, and punts 49 yards
• Team B starts on the 50 yard line, gains 0 yards, and punts 49 yards
• Team A starts on its 1 yard line, gains 0 yards, and punts 49 yards
• Team B starts on the 50 yard line, gains 0 yards, and punts 49 yards
• and so on until the end of regulation
While this would never happen so perfectly in real life, it creates a scenario in which each pair of drives results in a 49 yard field position differential. If we extrapolated this over 10 drives for each team, we might think that Team B has created 490 yards in "hidden yardage", but we also know that something is not right about that. Each Team in this hypothetical had the same success rate, same explosiveness, and same special teams play (though props to Team A for successfully punting out of its own endzone the entire game), but Team B didn't magically create that much hidden yardage. In fact, it didn't create any hidden yardage at all. Another way to look at this is that we have no way to explain the offset of the supposed 490 yards (i.e. why did the game still end regulation 0 to 0 with all those hidden yards?).

I am not trying to say that hidden yardage doesn't have a place in analytics. In fact, I think average starting field position tells us a lot about how a game unfolded. However, I am cautioning against turning the difference of average starting field position into something that it is not necessarily equal to, such as "hidden yardage".

So, is there a better way to calculate "hidden yardage", or the yardage that is effectively given to the offense through defense and special teams? Maybe, but it might require more situational awareness or, more likely, more of a focus on turnovers and special teams play, which I think was the point of the metric in the first place.

Note: I likely screwed a lot up in this post. If you notice something, point it out and I'll gladly fix it. My hope, though, is that the point I'm trying to make is more of the focus than the specific stats or calculations that I made, unless I am completely missing something.