There are a lot of interesting things about the results.
- Of the 30 RBs drafted in the first round in this time range, 20 weighed 215+ pounds. Of the 10 who did not weigh at least 215 pounds, every single one had a 40 time below 4.50. The average time for sub 215 backs was a blistering 4.37. Not surprisingly, the two lightest backs (CJ Spiller and Chris Johnson) recorded the two fastest times (4.27 and 4.24). BMI is also a good predictor of 40 time, as the 4 lowest backs on the BMI scale (CJ2K, Spiller, McFadden, Bush) had four of the five fastest times (Jahvid Best is the other). What this all amounts to is that if a RB is undersized, he needs to be very fast to get picked in the first round. This explains why guys like Gio Bernard and Ameer Abdullah did not crack the first round. They are not nearly fast enough for how small they are. Likewise, Paul Perkins (208 / 4.54) and Wendell Smallwood (208 / 4.47) also probably suffered from this. Perkins is not nearly fast enough for how small he is. Smallwood is closer, but every back who ran 4.47 or slower weighed at least 215 pounds and the average weight is a lot higher.
- Speaking of 40 times, 21 of 28 backs picked in the first round in this sample had a 40 time under 4.50. So right away you know that the league does not like to spend 1st round picks on backs who don't have great speed. Of the 7 backs who managed to get picked in the first round despite modest 40 times, the average weight is 222 pounds. This is significantly higher than the overall average for first round backs (which is about 217 pounds). What this suggests is that you are only "allowed" to get away with a slow 40 time if you are big. In other words, backs who don't have good speed must be big. And even big backs must still be relatively fast. Only two backs out of 28 who ran for scouts had 40 times slower than 4.60 (Mark Ingram and Cedric Benson). That's less than 10% of the backs in the sample and, anecdotally, I think there's a pretty good argument that both guys owe some of their draft slot to playing at massive college programs that rank among the best in the country at producing NFL talent. Small school prospects are often underdrafted and I think there's a decent argument that the opposite can happen (playing at a visible school like Bama, Georgia, or USC can lead to exaggeration of talent and overexposure). The requirement that big backs still be fairly fast probably explains why Eddie Lacy and Jeremy Hill were not first round backs. Hill ran 4.66 at the combine. Lacy ran 4.64 at his pro day. Either time would be the slowest of any RB picked in the first round in the sample. LeVeon Bell's 4.60 was theoretically within range of what the league has been willing to draft. However, it would be near the very bottom of the group and the 40 is only one drill. I would guess that his dismal marks in the other tests hurt him as well. His 31.5" vertical would be tied for the lowest of any back on the list and his 9'10" broad jump would rank near the bottom of the sample (his 6'1"+ height makes that mark especially bad because tall guys have an advantage in this drill).
- I could say more, but a lot of this can be summed up by saying that first round RB picks are usually reserved for backs who offer either elite speed or an elite combination of size and speed. The league very rarely uses first round picks on backs who don't run below 4.50 and/or weigh 215+ pounds with solid marks in the 40, vertical, and broad jump. This year's only first round RB, Zeke Elliott, has an above average weight (225) combined with a 40 time (4.47) that is near the middle of the entire first round RB group. He has a rare combination of size and speed. So although his marks in the jumps were quite terrible, he still roughly fits into the recent historical trends of what a first round RB looks like. I think there's an argument that his reputation has been inflated by his program ala Ingram/Benson, and that he wasn't worth the pick Dallas spent on him. Still, his 4.47 40 time at 225 pounds is a rare speed score.
- That all being said, necessary ≠ sufficient and the presence of elite combine numbers alone doesn't guarantee a first round draft slot. You mentioned Christine Michael. Why wasn't he a first round pick? He wasn't even a full-time starter in his final year at Texas A&M and had serious production/durability question marks. Scouts look at things besides size/speed/explosiveness and if a player doesn't pass the sniff test, he can still fall despite being a workout monster.
There are always going to be exceptions and people are going to accuse me of twisting the numbers to fit a narrative, but I think there's a pretty clear argument that the NFL does not like to invest early picks on RBs unless those players have obvious special traits. It's probably not a coincidence that the only backs selected in the top 100 this year (Elliott, Henry, Drake, Prosise) all offer something a little extra in terms of size, speed, or both. Like I said previously, you don't pay Mercedes prices for a Honda. Smart NFL teams are not going to burn an early pick at this position unless they're getting a player who gives them something that's hard to find.
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