How valuable are returning starters and what positions are they most valuable at

Just finished cleaning up my database for the 2009 football season and got 2008 added as well.  Hopefully will have the other 5 years or so of play by play data that the NCAA's website posts added to my database before football season starts, but its mindless data entry and I can only handle so much at a time! 

For now I wanted to compare 2008 vs 2009 and see how valuable it was to have returning starters and what positions it mattered the most at.  To this I used my opp adjusted team values (explanation here) from 2008 and 2009 as well as the handy Phil Steele Returning Starts* by position by team. To make the data manageable, I grouped the 120 FCS teams into deciles of 12 teams each, and used them as a composite group.  The least experienced teams would be decile 1 and the most experienced would 10.  I then looked at how much the returning starts meant for both outright success and improvement vs prior year as measured in points/game.

*I used returning starts as opposed to starters because there is a little more depth and separation to the numbers then.  7 returning starters could be 50 returning starts or it could 150 depending on how long some of the players had been starting.

Quarterback

Bottom two deciles = death!

Teams in the bottom two deciles, on average, were 4.1 points per game (3 points per game = about 1 win over the course of a season) worse in 2009 than they were in 2008.  In essence, this was Michigan 2009.  Technically, Michigan fell into D3 thanks to the valuable returning starts of Nick Sheridan.  Michigan's 8.4 pts/game offensive improvement was 2nd best nationally of any team returning less than 10 starts at quarterback. 

Overall, the impact of a returning QB starts goes beyond the passing game.  Each decile of experience is worth about a quarter of a point per game passing, but about a third of a point a game per decile on total offense.  Moving 5 deciles in experience is worth about a 1.5 a game for the offense.

Running Back

No position on the field came close to running backs in terms of lack of value for returning starts. 

There was literally no correlation from returning starts from running backs to on field success.  No improvements in running game or total offensive output. 

Michigan certainly has some questions at running back going into this season, but there is nothing in the numbers from 2008-2009 that says that bringing in an untested face at running back is a red flag.

Wide Receiver

This was the position that shocked me.  I always considered the wide receiver position to be largely talent driven with little thought given to the value of experience for receivers. 

In one of the strongest correlations I found, each decile of returning wide receiver experience was worth a half a point per game improvement.  Even more surprising, the improvement wasn't restricted to the passing game.  Of the half point improvement, only .3 ppg could be attributed to the passing game.  Veteran wide receivers play a huge role in a team's progress.  This may have been a fluky correlation for 2008-2009 but within the data set, it had one of the highest R squared values I found at 0.72.

Offensive Line

This was one of the hot theories going into last year, even sparking a Wall Street Journal article singing its praises.  The hidden secret to success was returning offensive line starts. 

What did I find, not that much.  I found that like quarterbacks, if you are in the bottom 20% of returning starters, your offense is in trouble, but beyond that, there wasn't much fire to the smoke.  Among the top 8 deciles, there was almost no correlation between returning OL starts and offensive success.  In fact, the top 20% of teams in returning starts were on average worse offensively in 2009 than in 2008.

Offense Overall

After breaking down the position groups, I took a look at the offensive unit in total.  There were two interesting trends that popped out in the aggregate look:

1. Either you are in or you are out, there is no in between.  The top 50% was 2 ppg game better than the previous season, whether they were in the 6th or 10th decile.  The bottom 50% was 2 ppg worse than 2008, whether they were 5th decile or 1st.

2. Overall returning starts plays a huge role in the running game. Even though running back returning starts didn't matter much, the totality of the offensive's returning starts had a third of a ppg per decile correlation with a 0.92! R squared value, the highest of any metric I looked at.

Defense Overall

Defense is a bit more of a fluid group, so although I looked at them individually, it seemed best to talk about them together.  Returning starts from the defense in total were much more valuable than returning starts from any single position group.  And like the offense, the biggest observation about the defense is that you don't want to be at the bottom of the food chain when it comes to returning starts.  The teams with the fewest returning starts were again, 5 points worse per game than even team in the bottom third. 

By position groups, the values were not as strong by position group as they were on offense.  There was also more intuitive results on the defensive side, DL starts were most valuable against the run, DB starts most valuable against the pass and LB in between on both.

Team Overall

Returning starts don't matter as much as people think.  The way they are most likely to affect a team is if you have very few.  A whole host of returners isn't necessarily more valuable than a solid group.  Just don't be stuck at the bottom, even a low ranking in a single position group can be worth a game or two. 

In the big picture, there is no difference between the 2nd decile and the 8th decile.  The 1st decile (last year anything less than 200 returning starts) was an unmitigated disaster, with only 3 of the bottom 12 improving at all and 4 of 12 showing double digit declines.  On the top end, the 9th and 10th decile were the only groups to show separation from the pack, but nothing like the separation at the bottom.

Side Note on turnovers

This topic has been covered very well on this site previously, so no need to add much more to it than to agree and say, turnovers are random!  Both forcing them and committing them shows virtually zero correlation from one year to the next.  If anything there is a slight negative correlation between turnovers one year to the next.

Future Articles

Now that I have 2008 loaded, if there is anything anyone out there would like to see, please let me know.  I have a couple of ideas loaded up.  I now have player positions loaded for 2009 and can therefor compare the seasons of BG, Suh and anyone else to see how they stacked up to their positional peers and how good their seasons really were.  I am also planning a post on the luckiest and unluckiest teams of 2009.  Let me know what you want to see and I will put a diary or forum post with what I can.