This is part 2 of a series. Read part 1 here.
Since starting linemen tend to come disproportionately from the early portions of the draft, and most starting linemen have never played for another team, are highly drafted lines, good lines? Are homegrown lines generally better than those stocked through free agency? For this post I'll use Football Outsiders' adjusted sack rate, and adjusted line yards to judge the quality of offensive lines around the league, not a perfect gauge by any means, but it's objective and includes as little influence from the rest of the team as is possible for a position that's defined by helping teammates to succeed. In measuring draft position I used both overall pick and the trade value chart's weighting of the overall pick. How well does starters draft position match up with the 2010 line stats? There are actually a few decent relationships.
Do more highly drafted lines outperform their counterparts consisting of lower drafted linemen? The 2010 data gives a clear "No!" 18 relationships between draft status and either sack rate or line yards were tested. Of the 12 which reached the 0.1 threshold to be considered a weak correlation 11 of them pointed towards lines of lower draft status as performing better. Of those 12, 4 relationships had a moderate correlation (0.3 or more), all of which showed a trend towards lower drafted lines being superior. The negative relationship between draft status and OL performance was strongest on the interior lines rather than the tackles and in relation to sack rate moreso than line yards (the one correlation in favor of more highly drafted linemen was line yards to average overall pick of the OTs).
A quite surprising result! What does it mean (if anything*)? Are highly drafted linemen actually worse? Are GMs around the league so bad at identifying OL talent that they take worse players earlier in the draft and play them more often than their superior late round counterparts? I wouldn't jump to that conclusion and here's why.
The drafts from 2002 to 2010 cover the selection of 112 of our 132 drafted linemen starting in 2010 and 380 linemen total. Just over 80% of the linemen drafted in the 1st round of those drafts started 9+ games this year. For 2nd rounders in that span it's 52%. About 1/3rd of the 3rd rounders were 2010 starters. The 4th and 5th rounders are both a bit under 1/4th. 12% of 6th rounders and 9% of 7ths were starting this year.
There are two ways I can think of to explain these two sets of figures together. Highly drafted linemen tend to get more chances than a similarly performing lineman with less invested in him and/or less raw, scout-enticing talent. Also that when drafting an offensive lineman early in the draft it's more of an assurance that you are getting a lineman who is at least starting caliber, than an expectation you'll have an elite talent. I tend to believe both are true. Projecting a players' development is no easy feat. A highly drafted lineman hits the starting lineup quickly and gets plenty of time to develop as a player. Later round picks quickly wash out if they don't improve, leaving the majority of highly drafted linemen starting somewhere whether they deserve it or not while the later round picks starting in the league are guys that have proven they can hack it in the league and better themselves as players.
A highly drafted line is far from a guarantee of good line play, with a number of lines made up of less highly touted linemen performing quite well. Taking a lineman early is very likely to net you a starter, but little assurance of their quality above and beyond that. Not that you should be scared away from the draft, be wary of free agent additions as well, a higher percent of starters who have played for other teams correlated weakly with a higher sack rate.
Next up: Where do good teams get their offensive linemen?
*= correlation does not equal causation, so "nothing" is quite possibly the right answer.