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I get your point, but that problem should be (largely) resolved by the regression. If heavier players are able to run as fast as lighter players, then there’d be no relationship between weight and speed and no one would get a boost. However, the regression proves that there *is* a relationship, so we should credit the fast and heavy players accordingly.

Now could you argue that it’s easier to decrease your time by “10 pounds” when you weigh 250 compared to 190? Probably! But as Jim Zorns said, players that are both heavier *and* faster are more valuable! And to that point I think the bigger issue is this metric is more useful for some positions than others.

For instance, I don’t know how much I care about a WR’s weight adjusted 40. I think DeSean Jackson’s pure speed is more valuable than if he were both 10 pounds heavier and slower. But I do think it’s telling for players that rely on both size and speed, notably DEs, TEs, and RBs. That’s presuming weight is a good proxy for their abilities in the run game, speed for the passing game, and weight adjusted 40s a good proxy for both.

I think this metric may be best used to help put the elite prospects in context – if you think someone is great *and* they test well in this metric, you’re probably right (see Donald, Clowney, Elliott, Beasley, CJ2k, etc) but it isn’t reliable on its own.