Standardized completion percentage gives truer version of accuracy

Before last year’s draft, ESPN Stats & Information highlighted a stat called standardized completion percentage, which is designed to capture a quarterback’s accuracy better than any traditional statistic.

The premise of the stat is that not all passes are created equal: A screen pass is easier to complete than a 20-yard out route, so a player who throws a lot of screens could have an inflated completion percentage.

Standardized completion percentage gives a quarterback credit for completing those short passes, but the credit he receives depends on how often an average quarterback would throw that pass. At its core, standardized completion percentage is similar to effective field goal percentage in basketball because it accounts for the distance of a quarterback’s pass, just as effective field goal percentage accounts for both 2- and 3-pointers. This stat also eliminates dropped passes and throwaways, because drops are not the quarterback’s fault and throwaways are generally a good decision.

Evaluating the accuracy of NFL draft prospects using traditional completion percentage is nearly impossible because of the varying offenses run in college. Standardized completion percentage not only is a better measurement of accuracy, but it also has been shown to be a superior predictor of NFL success.

In the last three seasons, the top three players in standardized completion percentage entering the draft were Russell Wilson, Robert Griffin III and Teddy Bridgewater. All three have had above-average Total QBRs since entering the NFL and have a combined 56-39 regular-season record.

Meanwhile, among players drafted in the first three rounds since 2011, the bottom three players in standardized completion percentage were Mike Glennon, Geno Smith and EJ Manuel. Those players all have below-average QBRs in the NFL and have combined for a 22-39 record.

Smith and Derek Carr are great examples of the value of standardized completion percentage. In their final college seasons, each player led the nation in screen passes and ranked in the top eight nationally in completion percentage. Once accounting for the distance of their passes, their standardized completion percentages were among the worst of the draft-eligible prospects, and both have struggled with accuracy in the NFL.

Looking forward to the 2015 draft class, Marcus Mariota is the most accurate quarterback of the group. He completed 68.3 percent of his passes with an average pass distance of 8.8 yards last year at Oregon. That resulted in a standardized completion percentage of 73.6 percent.

Mariota’s accuracy has been pegged as an area of concern as he transitions to the pros. The numbers do not support this notion. He led all Power 5 quarterbacks in completion percentage on passes thrown 15 yards or longer last season and ranked second in completion percentage from inside the pocket. Although standardized completion percentage does not account for Oregon’s offense and how often Mariota was asked to read defenses, it captures his accuracy on the throws he was asked to make.

Overall, the 2015 class is less accurate than the 2012 or 2014 classes. Mariota has the highest standardized completion percentage of the group, but he ranks behind Wilson, Bridgewater and Andrew Luck when they came out of college. Other accurate quarterbacks in the 2015 class include Kansas State’s Jake Waters (72.6 percent), UCLA’s Brett Hundley (71.6 percent) and Colorado State’s Garrett Grayson (71.0 percent).

Among the top 15 FBS quarterbacks based on Scouts Inc. ratings, Duke’s Anthony Boone has the most concerning standardized completion percentage (58.3); he was one of the least accurate quarterbacks in the country. Oregon State’s Sean Mannion regressed considerably from his junior season. His 2014 standardized completion percentage of 67.7 is lower than that of any player drafted in the first three rounds in the last three draft classes.

No one college metric will be able to predict quarterback success in the NFL. But this take on completion percentage, which is often misleading in college, is a truer measure of accuracy and can tell a lot about how a player will adjust to the NFL -- a league where accuracy is essential to a quarterback’s success.