Frank Gore: Looking back, looking ahead at the 49ers running back

How much longer can Frank Gore continue to be Frank Gore? It's a question that we've had to ask ourselves for the past several seasons and one that will continue to be asked until he's gone. Considering the San Francisco's offensive style and the uncertainty – not necessarily good or bad, just unknown – at the running back position beyond Gore, it's also one of the most important questions facing the 49ers headed into the 2014 season.

Several of my NN brethren have, in this very Internet space, explored this question since we closed the book on the 2013 season. But talking about Frank Gore should be a fun break from court dates, plea deals and the pre-draft hysteria that's been going over the last several weeks (months?). So talk about Frank Gore we shall.

Before delving into Gore's prospects for the upcoming season and beyond, I thought it would be fun to take a gander back at Gore's career thus far and attempt to put it in some sort of context.

Frank the Tank, a Retrospective

Since coming into the league as a third round pick in 2005, Gore has been among the most effective and reliable backs in the league. No other running back has played in more games than Gore in that post-2005 time frame, which seems especially notable considering Gore's reputation – both entering the league and throughout much of his career – as an injury risk, with his reconstructed knees supposedly due to melt at any time. Over that same span, only Steven Jackson has carried the ball more often that Gore and just Jackson and Adrian Peterson have accumulated more rushing yards than Gore's 9,967.

Assuming Gore finishes even a single game in 2014, he'll crack the 10,000 career rushing yardage milestone, becoming the 29th player in NFL history to do so. In all but the very worst scenarios for the upcoming season, Gore will break into the top 25 on the all-time rushing yardage leader board. At least by traditional measures, Gore has piled up some impressive career totals. Just for reference, here they are in table form (along with some additional, more advanced numbers which we'll be getting to later):

Looking over those numbers, one thing you might notice is how consistent Gore's production has been, at least in terms of rushing yards. There's a massive spike from his rookie campaign, in which he was just a part-time player behind Kevan Barlow, to his second year, his first as the starter. But after that, things level off to around 1,100-1,200 yards per season, or 75-80 yards per game. There isn't a point in which you would say that Gore was the best player at his position, but he was consistently among the top handful or so. And I think we all feel pretty confident in the idea that Gore's numbers were deflated early on by some of the most inept offenses in league history.

As far as I can tell – and I certainly haven't done extensive research in this area – this type of career curve is a bit atypical for running backs. A good amount of research has been done on running back aging curves – recently, Chase Stuart has looked at this topic a couple of times over at his site, Football Perspective – and most that have done that research have come to some similar conclusions. Most backs see the bulk of their production come early in their careers, peaking somewhere around 26-28 years old before steadily declining for the remainder of their career. Of course, few backs follow that progression exactly. Many are lucky to be playing a significant role, if at all, by the time their age-28 season comes around. Fortunate backs might see a bounce back year late in their career before falling off for good. And then you have the rare backs that are able to remain productive into their early 30s.

As you can see from the above chart, it's difficult to pinpoint a clear peak for Gore's career. Looking at several other statistics also prove to be mostly inconclusive. Gore's yards per attempt have bounced back and forth on almost a yearly basis between the low and high fours. His success rate, as measured by Advanced Football Analytics, also fluctuates largely from year to year.

The two metrics that paint a different picture for Gore's career arc are Football Outsiders' DYAR and DVOA. Both of FO's core metrics show the same large jump in performance from Gore's first to second season as we saw above when looking at rushing yardage, which obviously makes sense. But it's from that point that DYAR and DVOA diverge from the more traditional metrics that we looked at previously. There's a pretty clear, gradual decline from that monster sophomore season through Gore's age-28 season in 2011. Then we get a massive rebound year in 2012 built on a historically efficient start to the season followed by things coming back down to earth a little last year.

Regardless of how you want to measure up Gore's career, it's clear that he has been the best and most productive back in franchise history (#respect to Roger Craig and the Million Dollar Backfield). His place in the Edward J. DeBartolo 49ers Hall of Fame is secured even if his place in Canton is a bit murky. It's going to be a terribly sad day in Ninerland when Gore is no longer donning the red and gold.

So far, we've simply stated the obvious. I'm sure many of you are very familiar with Gore's various accomplishments and milestones. That's in the past. Now, with all of this data at our disposal, let's attempt to craft somewhat of a best-case and worst-case scenario for Gore's upcoming season.

Making the case for a washed-up Gore

We all know that this season is lurking out there somewhere, just waiting to break all of our hearts, even if we refuse to admit it. Gore is entering his age-31 season. History has not been kind to running backs on the wrong side of 30. According to the previously mentioned Chase Stuart research, running backs, assuming they recorded at least 150 carries in each season, have lost an average of just about 200 yards in their seasonal rushing total from their age-30 to age-31 seasons. That type of drop for Gore would send him under the 1,000-yard mark for just the second time since he took over as the 49ers' primary ball carrier.

There are other signs of decline beyond just the standard "old running backs suck" stuff. Gore's yards per carry, at 4.1, reached a career low last season leading to the lowest yards per game mark since his rookie season. His success rate fell to 37.5 percent, also a career low number.

Perhaps most concerning was that Gore suffered a significant drop in the rate at which he broke tackles and gained yards after contact. Pro Football Focus has data going back to 2007, Gore's third season in the league. Gore's yards after contact per carry fell to 2.00, easily his lowest mark in PFF's data set and down from 2.64 the year prior. PFF has another metric they call Elusive Rating, which essentially combines the rate at which a running back forced a missed tackle with yards gained after contact into a single number to give you an idea of how difficult the back was to bring down. Gore's elusive rating in 2013 was the third worst number among qualifying backs, and again was easily the worst figure of his career. Gore had never dominated either one of these metrics, but typically found himself right around the middle of the pack. If Gore has lost the ability to make defenders miss at the same rate we've become accustomed to, that obviously doesn't bode well for the likelihood of him continuing to put together successful seasons.

Getting back to DYAR data mentioned a few paragraphs ago, you can make the argument that Gore has already been on the decline for several years now, somewhat dismissing his 2012 season as an outlier in which everything, including that insanely efficient start, just so happened to break his way. Prior to that great 2012 campaign, Gore had finished below replacement level for two straight seasons, bottoming out in both DYAR (-17) and DVOA (-10.0%) in a 2011 season that saw the running game account for an inefficient bulk of a hyper-conservative offense.

Putting all of that together, it's not difficult to make the case that the terrible Frank Gore season from our nightmares is looming right around the corner. His efficiency has fallen, he's no longer making defenders miss and there are three young running backs behind him on the depth chart itching for more playing time.

One Last Hurrah

With that painful exercise out of the way, let's move to making the case for another productive Frank Gore season. Focusing primarily on rushing yardage, what Gore has done in his three seasons between the ages of 28 and 30 has put him in some select company. During the past three seasons, Gore has played in all 48 regular season games while rushing for 3,553 yards on 816 carries, giving him an average of 4.35 yards per carry. Rather than looking at what all running backs did at 31 years old and using that to try and project what Gore's season might look like in 2014, it makes more sense to look more specifically at players that put together similar stretches in the three seasons leading up to their age-31 season.

With that in mind, I looked for players who had age-28 through age-30 seasons meeting the following criteria:

• Played in at least 36 of the 48 possible games
• Carried the ball at least 600 times (200 per season)
• Averaged at least 4 yards per carry
• All three seasons took place after the NFL-AFL merger in 1970

Those requirements should ensure that we find players who were primary options of similar caliber to Gore. Using the immensely helpful Pro Football Reference Play Index, my search returned a list of just 24 players (including Gore) meeting our criteria. Of those 24 players, two just finished their age-30 season last year and have therefore yet to play in their age-31 season (Gore and Steven Jackson); two did not play after their age-30 season (Barry Sanders, Michael Turner); and two more played so little in their age-31 season that it didn't make sense to include them in our sample (Shaun Alexander, Chuck Muncie). That leaves us with 18 players from which to analyze their age-31 season.

Our 18 player sample put together an average line of 242-1,019-4.21 (carries-yards-average) while playing just over 14 games. At the top end of the sample, Curtis Martin (1,697 yards), Walter Payton (1,684), Tiki Barber (1,662) and Thomas Jones (1,402) had career years in their age-31 season. At the bottom of the list Fred Jackson (437), Eric Dickerson (536), Charlie Garner (553), and our very own Roger Craig (590) battled injuries, became part-time players or both. That's a wide range of outcomes, which is to be expected given the small sample that we're dealing with. However, we do have some precedent for higher-quality backs experiencing success beyond the age of 30.

One thing that could help Gore's odds of another productive season out immensely would be more willingness to spread things out on offense and create some additional room in the box. A few weeks back, Pro Football Focus looked at how running backs fared against various defensive packages. With 95 percent of his carries coming against fewer than five defensive backs – 15 percent of that came against fewer than four with both numbers "leading" the league by a comfortable margin – no one faced more heavy defensive personnel groupings that Gore did last season. This is shocking to absolutely zero 49ers fans.

According to PFF's data from the same article, over the past six seasons backs have averaged 4.2 yards per carry against defenses with four defensive backs and 2.3 yards per carry facing those with three. Putting Gore's 4.1 yards per carry number in that context makes it look a bit better, coming in at essentially league average. Gore's 4.3 yards per carry against base defenses was good for the 12th best mark in the league. Consider that San Francisco faced the third most difficult schedule of opposing defenses by DVOA and it looks better still.

The 49ers offensive sets have put Gore at a significant disadvantage compared to much of the rest of the league. Even on the low end, most other backs are facing Nickel or Dime defenses on 15-20 percent of their carries. On the high end, Reggie Bush, Knowshon Moreno, LeSean McCoy and Danny Woodhead all saw defenses with at least five defensive backs on the field on over three-quarters of their carries. Harbaugh and co. are never going to make that drastic of a change in their offensive philosophy, but an increased effort to get teams out of their base defense, therefore freeing up space in the box, could be a nice boost to Gore's efficiency. Getting that fifth defensive back on the field is worth about an additional half yard, per PFF's data. Get a sixth defensive back on the field and you can tack on another yard per carry.

The Frank Gore we saw as recently as 2012 is dead and buried. Frank Gore, 2013 edition, is still a real possibility though. If the coaches can give him some more advantageous situations to run in and we can get a bounce back year from the offensive line – which I haven't touched on at all, but they were definitely worse a year ago than they were in 2012 – and we just might have found our recipe for another 1,200-yard season from our beloved running back.

Looking beyond 2014

We've outlined a couple of reasonable scenarios for what Gore's 2014 season might look like, but can we speak at all to what we can expect a bit more long term? Using the same sample of 18 players that we used above, I also looked at what each of those running backs were able to over the remainder of their career, including that age-31 season. As you can probably guess, the results weren't great.

As a group, our 18 running backs averaged 2,129 yards over the remainder of their career. That number is propped up a bit by Walter Payton and Emmitt Smith, both of whom tacked on over 4,000 yards to their career totals after the age of 30. As expected, yards per carry was down nearly across the board with the only notable exceptions of Tiki Barber (who averaged over five yards per carry in his one and only season after turning 31) and Fred Taylor (who had a very efficient age-31 season, averaging 5.4 yards per carry while sharing the backfield with Maurice Jones-Drew, before he proceeding to also fall off significantly). Our sample played in an average of 40 more games in their twilight seasons, typically playing out a couple of seasons with a vastly reduced role.

If we are fortunate enough to experience one more productive Frank Gore season, it will almost certainly be his last. His contract is up following this season and if San Francisco brings him back, it's hard to envision him having anything more than a complementary role. But we can worry about all that when the time comes. For now, let's sit back, crack open a beer and enjoy the greatest 49ers running back of all-time while we still have him, for as long as that may be.