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April 3, 2014

Some Comfort in a "Depleted" O-Line

Georgia's offensive line returns "only" 57 career
starts in 2014, but what does that total suggest,
if anything?
After posting on my Author-UGA football FB page a few days ago that the Bulldogs' 2014 offense might have the first "1-2-3 1,000-yard returning combination" in college football history, I received a text from a friend saying, "Now, if only we had a line to block for them..."
This season's offensive linethe unit is apparently going to be a weakness, or an area of concern, for an offense which otherwise is loaded in the backfield and at receiver, while engineered by a more than capable passer.

Why all the worry about the o-line?  According to one early preseason preview, the unit has been "depleted"; the Bulldog offense is lacking returning experience up front.  Returning experience along the offensive line is often measured by the unit's number of returning career starts, which I've blogged about before, and which Georgia has the "depleted" total of only 57 for 2014: David Andrews 27, John Theus 22, Kolton Houston 6, and Mark Beard 2.
Career OL Starts Returning (COLSR) has been recognized as a viable preseason evaluator for some time.  For example, the top two offensive lines in college football entering last season according to Phil Steele, "the Guru of Formulation and Prognostication," happened to be the top two offensive lines in career starts returning, as well.
In addition, I've also blogged before about the Offensive Hog Index, which was originally an NFL comparative measurement for offensive line performance.  I tweaked the index to where a college team's offensive line ranking is determined by its average of the following three rankings in comparison to other teams being measured: yards per rush (sacks omitted), percent of passing plays (pass attempts + times sacked) resulting in an interception or sack, and third- and fourth-down combined conversion rate.

Georgia's apparently lowly total of 57 entering this season compelled me to figure whether COLSR was any sort of indicator of how well an offensive line would perform as a group, and most importantly, its team's win-loss record in the end.  One might think so, at least to some degree.  However, I'm reminded of the 2010 season, when the Bulldogs had an FBS-high 155 COLSR.  I was hopeful the extremely high number of starts coupled with an above-average offensive line performance in 2009 would equate to success for Georgia's offensive line and the team overall.  Instead, the Bulldogs' Offensive Hog Index was actually lower in 2010, while the team's record dipped from 8-5 to 6-7.  Of course, that's just one example.

Beginning with the 1995 seasonthe first year Georgia's offensive sacked totals are available (to figure into the Offensive Hog Index)through 2013, I've listed the Bulldogs' COLSR entering each year, followed byàthe team's record at the end of the season, and its Offensive Hog Index in parenthesis.  To make things as balanced as possible, I added the bowl statistics (while perhaps adding to the confusion) into the seasons before 2002 when bowls weren't recognized in season totals.       
YR:  OL stsàRec. (Index)
1995:   58à6-6 (11.2)
1996:   47à5-6 (2.3)
1997:   37à10-2 (14.7)
1998:   38à9-3 (6.0)
1999:   39à8-4 (10.3)
2000:   50à8-4 (6.8)
2001:   58à8-4 (7.0)
2002:   98à13-1 (7.0)
2003:     4à11-3 (6.0)
2004:   74à10-2 (12.8)
2005: 134à10-3 (11.3)
2006:   68à9-4 (5.7)
2007:   25à11-2 (16.3)
2008:   24à10-3 (15.0)
2009:   99à8-5 (10.3)
2010: 155à6-7 (9.5)
2011:   86à10-4 (8.0)
2012:   31à12-2 (14.3)
2013: 101à8-5 (15.3)

For example, Georgia entered last season with 101 COLSR; they would finish with an 8-5 record.  The Bulldogs' 15.3 index is an average ranking (points) based on their 5.06 rushing average, which was the 2nd-highest for Georgia in the last 19 seasons (or 18 points earned); their 7.07% of negative passing plays was 7th-best of 19 (13 points); and their 43.85% conversion rate on third and fourth downs combined was 5th-best (15 points), for an average of 15.3 points. 

After a quick glance at the numbers, the first thing I noted was that it seemed 57 COLSR wasn't all that low when comparatively speaking.  Indeed, come to find out, Georgia has averaged just a bit higher at 64 COLSR entering the last 20 seasons.  However, as far as discovering if COLSR was any indication for the success of a team and its offensive line, I was going to have to go even further in depth, and get a little nerdy with the numbers.
Familiar with the correlation coefficient?  Personally, I had never even heard of it before finding it yesterday in a Google search.  Basically, it can measure the degree to which two data sets are related, resulting in a number between -1 (an absolute negative correlation) and 1 (a perfect positive correlation).  The closer a correlation coefficient is to 0, the more there is no relationship between the data.  
COLSRàHog Index: I first wanted to see if there was any relationship between Georgia's COLSR entering the last 19 seasons and the team's offensive line performance, or Hog Index, at the end of each respective year.  And, perhaps surprisingly to most, there was none whatsoever.  In fact, with a correlation coefficient of -.026, there was a very slight negative correlation. 
COLSRàFinal Record: One might think there would be some positive correlation, even the slightest, between COLSR and a team's final record.  On the contrary, the opposite actually holds true for Georgia.  To demonstrate, and why this relationship had a correlation coefficient of -.319, which is considered very close to a fairly negative correlation, check this out: Georgia's top four seasons of COLSR2005, 2009, 2010, 2013yielded an average record of just 8 wins and 5 losses, whereas the bottom four2003, 2007, 2008, 2012remarkably wound up with an average record of 11 wins and 2.5 losses.
Hog IndexàFinal Record: Finally, a positive relationship is found between Hog Index and final record, and a fairly substantial one at 0.339.  And, it certainly makes sense: the better the offensive line play, the better the team's record, and vice versa. 
What might not make sense is my use of all these figures, statistics, coefficients, and such.  Although, one thing is for sure in my opinion: when it comes to Georgia's offensive line the last two decades, the only indicator of its role in the team's overall performance is the unit's play on the field, and not whether its an experienced group, or one depleted.


Anonymous said...

Injury could also be a variable between the starting grade and the winning percentage. That would bring us back to the depth issue. I guess part of depth might be calculated into the number of starts but more than likely, game appearances would be a better indication of experience for the backups.

Anonymous said...

great post as always, Patrick. I've noticed before steele and others on the net like to use OL starts returning to help forecast. just goes to show that Georgia, like with a lot of tendencies in college football, often bucks the trend. always like it when you get nerdy with the numbers ; ) thanks for your hard word! - jay