The stake in the ground of the Blind Side Project is that time in the pocket, which is increased by good offensive linemen, has a significant effect on a QBs ability to complete passes. The natural first pass at trying to establish this would be to look for a direct correlation between completion percentage and time in the pocket while adjusting for the distance of the throw. While a small positive correlation can be found, it does not seem to be of the magnitude one might expect, or at least I would not expect. This could be a function of the size of the data set, and that more data will demonstrate a stronger correlation, but I think that the complexities of the game of football, are more the culprit. There are a host of factors that could effect the relationship between time in the pocket (even adjusted for distance of the throw) and completion percentage. One area that is clear however, is that when a QB is under pressure, their completion percentage (adjusted for the distance of the throw) drops. In our 2007 data, when Peyton Manning is under pressure, his adjusted completion percentage drops from 86% to 46% and when Tom Brady is under pressure, his adjusted completion percentage drops from 71% to 39%. There is also a very direct connection between how long a QB holds the ball and the probability that they are under pressure. The graph below demonstrates the "survival function" or the estimated probability that a QB will not be under pressure, for any given length of time in the pocket.
This helps provide a baseline for the overall quality of an offensive line. Lines (or individual linemen) that can help increase this probability, can help increase the overall efficiency of the offense. Additionally, linemen that can increase the No Pressure probability, also provide the playcallers with increased flexibility in areas such as depth of routes and number of receivers running routes (as opposed to staying in to help block).