The Harvard Sports Analysis Collective has just released a study of what combine results have statistically led to success in the NFL. They looked at a large number of NFL players and compared their actual performance in the league with how well they did in various tests at the combine, and the results are not always what one would expect. Let's take it by position:
QB: Only two stats matter in terms of predicting success for QB's -- they need to be over 6'2", and must have good shuttle times (which measure agility). Being 6'6" helps a little, but the main thing is getting up to the 6' 3" mark. (Keep in mind there can be "outliers" like Drew Brees who are shorter and still successful. What the Harvard model is saying is that if your QB is over 6' 3" he has a much larger chance for success.)
RB: They do best if they are short, heavy and fast (i.e., speed in the 40) at the same time. No metrics are predictive for FB's.
WR: Nothing that happens at the combine predicts success here. Speed does NOT matter, nor does height or leaping ability (see Welker, Wes). The traits that lead to great WR's are not measured in any way at the combine.
TE: Here is where you get your best predictions from combine performance. TE's will perform better if they have good 40 times and bench press a lot of reps. Agility, height and weight do not matter.
Center: Only the shuttle time is important. The bench press does NOT matter at all. Upper-body strength is NOT that important for Centers (although the Harvard people assume all NFL Centers have at least a certain amount of it).
OG: Speed in the 40, not agility, predicts best.
OT: Speed and size matter (weight, not height). Agility and strength surprisingly do not predict the success of OT's.
DE: Combine scores are also good predictors for this position. The heavier, faster and more agile (shuttle time), the better. This is the only position for which the cone drill is relevant.
DT: The heavier, stronger (bench press) and more agile (shuttle time), the better, but the predictive value is nowhere nearly as good as it is for DE's. Height and "explosiveness" are NOT factors.
LB and FS: The combine is useless in forecasting success at all of these positions. Forget it.
SS: Again the combine is of little value, although faster SS's do fare better in the NFL, along with those who are lighter (it's counterintuitive, but you don't want a lot of weight at this position).
CB: Here the combine does help predict outcomes. CB's with better 40 times who do well in the shuttle drill and are heavier do the best. Vertical leap and height do NOT matter.