top 4: Todd Gurley, Nick Chubb, Josh Robinson, and Tevin Coleman. I'm a little surprised to see Gurley there - he did pretty well in
my elusiveness numbers but wasn't that close to the top. Not at all surprised about the other 3: Chubb & Robinson are the top 2 in my numbers (though in a small sample size), and Coleman was near the top in my numbers (and I'd expect him to do better in yards after contact than in my capped yards after contact metric, since he broke several long runs that included a broken tackle).
I don't know how you come up with your numbers, but Gurley breaks more tackles than any RB I can remember in recent years. Some games, it seemed he broke a tackle every time he touched the ball. I can't see any way he would not score well in this type of ranking.
Here's a sample of how I come up with my number: Gurley's first 8 carries against Auburn in 2014, which are in
this video from 0:53-2:11.
On his first carry, a defender catches him in the backfield near the 32 yard line, fights through the stiff-arm, and succeeds in bringing Gurley down short of the 35. This goes in my books as "s 0 3" - it started out in space rather than traffic (Gurley had just one defender to beat, and room to maneuver), Gurley broke 0 tackles, and he gained 3 yards from where he was when the defender had the initial tackling opportunity.
On his second carry, the defender meets him in the backfield shortly after the handoff, between the 30 & 31, and he goes down between the 31 & 32. That goes down as "t 0 1" - in traffic (this is a bit of a judgment call, but Gurley didn't have much time to react after the handoff and a second defender closing in behind kept him from having room to cut back), 0 broken tackles, 1 yard after contact.
On his third carry, Gurley runs parallel to the line of scrimmage, fights off one defender near the line of scrimmage near the 20, turns downfield and slips through an arm tackle around the 15, and goes out of bounds around the 9. That goes down as "s 2 11" - in space, 2 broken tackles, 11 yards after the initial tackling opportunity.
At the 1:19 mark, Gurley faces a defender one-on-one as he tries to bounce it outside. He's just inside the 9 when the defender meets him, and he dives/falls/gets swung forward just past the 7. That's "s 0 2".
Next possession (after a touchdown pass), Gurley runs through a nice hole up the middle and is near the 23 when a defender first has a real shot at him. That defender jumps on his back, and he goes down at the 26. I counted that as "s 0 3" (space vs. traffic is a bit of a judgment call - there were other players in the area, but when a RB is at the second level running with a full head of steam I tend to lean towards counting it as "space" unless it's an extremely tight crease or multiple defenders are converging on him at once).
Next carry, Gurley runs into a pile of bodies around the 28, it seems to end up down at the 29. "t 0 1".
At 1:54, Gurley runs to the outside heading towards space, but two defenders close in to meet him near the Auburn 16. One defender dives for his legs, and it looks like Gurley might be able to bounce off it, but the other helps clean up. Gurley falls forward and ends up down near the 14. "t 0 2" (traffic because he was facing two defenders; no credit for a broken tackle if you're facing two defenders and you beat one while the other takes you down - and in this case it's not even clear that he did beat the one defender who went for his legs).
Next carry, Gurley runs straight into a body or two at the 15 and gets swallowed up and knocked back & to the ground. "t 0 0".
Those are his first 8 carries of the game. They go in my notes simply as:
s 0 3
t 0 1
s 2 11
s 0 2
s 0 3
t 0 1
t 0 2
t 0 0
If I had to use just one stat to measure elusiveness, it would be the one that I label YATOCAT - Yards After Tackling Opportunity Capped At Ten (aka capped yards after contact). Gurley had 22 yards of YATOCAT on those 8 carries (23 yards after contact, but the 11 YAC carry only counts as 10 because of the cap), giving him a 2.75 average.
That was a below average set of carries for Gurley - for that game as a whole he was at 3.15 YATOCAT, and for the 7 games I've charted he was at 3.35. But the main point here is to show the method, not to share a perfectly representative set of Gurley's carries.
Since I'm not limited to just one stat, I also calculate several others.
SYATOCA15 (aka capped space YAC). Gurley had 4 carries in space, and 19 capped YAC on those carries (the cap is at 15, so he gets credit for all 11 yards on that one carry), for a SYATOCA15 of 4.75.
TYATOCA8 (aka capped traffic YAC). Gurley had 4 carries in traffic, and 4 capped YAC on those carries, for a TYATOCA8 of 1.00.
Broken Tackle Rate. Gurley had 2 broken tackles on 8 carries, for a 25% broken tackle rate.
Space Broken Tackle Rate. Gurley had 2 broken tackles on 4 space carries, for a 50% space broken tackle rate.
Traffic Broken Tackle Rate. Gurley had 0 broken tackles on 4 traffic carries, for a 0% traffic broken tackle rate.
3+ Extra Rate (on plays without a broken tackle, the percent on which there were at least 3 yards after contact). Gurley had 7 carries which involved no broken tackles, and gained 3+ yards after contact on 2 of them, for a 29% 3+ Extra Rate.
Traffic 3+ Extra Rate (on plays in traffic, the percent on which there were at least 3 yards after contact). Gurley had 4 carries in traffic (including carries with or without a broken tackle), and gained 3+ YAC on 0 of them, for a 0% traffic 3+ extra rate.
The traffic vs. space distinction is there because it's much easier to break tackles and get YAC in space, and some offenses give the RB the ball in space a lot more often. If I didn't calculate them separately, the RBs who get the ball in space a lot would tend to look better. This also helps break down a runner's skillset - we can see in
my RB elusiveness spreadsheet that David Cobb did extremely well in traffic but was averageish in space, and that Ameer Abdullah did pretty well in traffic despite his small size.
The cap on YAC is there because, if a RB breaks a long run after breaking a tackle, that inflates his YAC stats a lot even though most of those yards don't tell us much about his ability to deal with contact. I use a higher cap for space (15) than for traffic (8) because it's common for a RB to drive forward several yards against a single DB in space before going down, and I want to give a RB who beats the defender and gets past him cleanly noticeably more credit than one who just pushes a DB back for a few yards and then falls forward.
The 3+ Extra Rate seems meaningful because it measures how well the RB is able to fight for the extra yard rather than being taken down cleanly. 1-2 yards after contact can come just from falling forward, but 3+ takes something more from the runner. Making a guy miss in space is a different skill, so I leave those carries out of this calculation. Broken tackles in traffic often do involve the "fighting for extra yards" skill, so I do count plays with a broken tackle in the Traffic 3+ Extra Rate stat.
My overall Hard To Tackle Rating is just a weighted sum of these stats (with the capped YAC stats getting more weight than the broken tackle stats which get more weight than the 3+ Extra stats), plus a strength of schedule adjustment. I wrote more about it in
this thread last year.