What is S2 in the NFL? Explaining the C.J. Stroud controversy driving doubt over 2024 draft cognition test

One year ago, an NFL cognition test placed C.J. Stroud’s draft stock in question. But the immediate success of the Texans’ rookie quarterback flipped the uncertainty back onto the test.

The S2, administered at the annual scouting combine, is not an intelligence test like the Wonderlic test of old. Instead, it is designed to measure the ability of players to make split-second decisions, a particularly helpful trait among quarterbacks.

Test scores are not made public, but Stroud’s test was leaked after the 2023 combine. Stroud underperformed on the S2, which graded him in the 18th percentile among quarterback prospects; eventual No. 1 overall pick Bryce Young graded in the 98th.

Yet Stroud went on to have a prolific rookie season for the Texans, throwing for the third-most passing yards (4,108) and the sixth-most touchdown passes (23) of any rookie in NFL history. He also boasted a 23-to-5 touchdown-to-interception ratio, becoming the first rookie in NFL history to pace all qualifying signal-callers in that stat.

MORE: When is the 2024 NFL Combine?

Many onlookers expected Stroud, taken by Houston with the No. 2 overall pick, to face a learning curve with a Texans team few expected to succeed. But he led that team to a 10-7 record, an AFC South crown and a wild-card win over the Browns.

Stroud’s immediate success — coupled with some struggles by Young — has the football world scrutinizing the test once believed to be the future for analyzing quarterbacks before the draft.

Here’s what you need to know about the S2 and the controversy surrounding the test.

What is S2 in the NFL?The S2 is nothing new to the NFL. It has been administered since 2015, and plenty of the top quarterbacks in the sport today have taken the test at the combine or as part of studies requested by teams.

The test is conducted on a gaming laptop or similar device (such as an Xbox). It works by testing for perception speed, visual search efficiency, trajectory prediction, impulse control and improvisation, per S2’s website.

Athletes spend 40 to 45 minutes on the exam. Test takers have their reactions recorded on a pad that can track reactions in two milliseconds, The Athletic reported in February 2023, which is a fraction of the time it takes for the eye to blink.

Those tests are conducted in different ways. For one, diamonds missing points flash across the screen in 16 milliseconds and users have to indicate on which side the diamond point is missing. Another test tracks the amount of objects athletes can remember. Another asks the users to quickly identify a specific object in a mixture of 22 figures.

“We’re talking about things they have to perceive on the screen within 16/1,000th of a second, which is essentially subliminal and which scientific literature says you shouldn’t be able to process,” Brandon Ally, co-founder of S2 Cognition, told The Athletic. “And I’ll be honest with you, we’re seeing pro baseball players see something way faster than 16 milliseconds, which has never been reported in literature, all the way to some athletes who may take 150 milliseconds. So our eyes may see the same thing. But for some, it takes longer to process than others.”

The most important of the various scores for quarterbacks are tracking multiple objects, decision complexity and improvisation. All different tests are graded separately, and a formula calculates the test-taker’s final score.

S2 controversyStroud and Young were vying for the title of top quarterback prospect in the 2023 class. But in April 2023, just before the draft, the S2 scores for the prospects leaked.

The leaked report showed Young with total score of 98%, while Stroud graded at 18%.

“Stroud scored 18,” an executive told Go Long. “That is like red alert, red alert, you can’t take a guy like that. That is why I have Stroud as a bust. That in conjunction with the fact, name one Ohio State quarterback that’s ever done it in the league.”

For his part, Stroud didn’t let it bother him. The Athletic reported he said he knew he was “about to get drafted regardless of that dang test.”

Some general managers have since called out the leaking of the score anonymously to The Athletic, with one saying it was likely a team that wanted to “gloat on what they wanted seen” and another calling it “complete B.S. that it was leaked.”

There was some speculation even from within S2 about Stroud’s test result. Though S2 would not publicly comment on Stroud’s actual result, The Athletic did report S2 had been flagged when Stroud’s test score came in and teams were told the score was “unreliable.”

“From my understanding, the S2 people had a lot of questions when his score came back in,” one executive told The Athletic. “It got leaked by a club, and they wanted to know why.”

Why “unreliable”? Several executives told The Athletic there was a belief Stroud did not put full effort into the test. There were several factors that could have led to that belief: He might have taken it at the end of a long day; he might not have been a great test-taker; he might have been nervous; he might have just not felt like it.

“It made us all say, ‘Wait a minute, what?’ You watch his tape, and his tape is awesome. He’s processing. He’s playing fast. He’s making good decisions. Maybe this is just an anomaly? Maybe he didn’t try?” an executive told The Athletic. “When it’s an outlier like this, you ask yourself, when and where did he take it? Was it his fourth test that day and he’d just had enough? Then you call the agent and say, ‘Hey, he scored really low on this. Can we get him to take it again?’”

For his part, Stroud had told The Athletic last fall that there are “some things I apply myself to, some things I don’t.” He explained he did well in school, but described himself as “lazy” in the classroom and that he would “get what I could get so I could play football.” He had nothing against S2 for the leak.

Plenty of others around the league were frustrated by it, however. Colts general manager Chris Ballard blasted the leak immediately following the 2023 draft and noted he thought Stroud “had to take a beating he didn’t have to take.”

As a result, at least one agency, Athletes First, has told its players not to take cognitive exams before the 2024 NFL Draft, The Athletic reported. Athletes First represents Stroud.

“We understand that many of your teams use these tests or protocols as part of your prospect evaluation process, however our recent experience with these exams has been less than positive,” an email from Athletes First to NFL teams read, per The Athletic. “Specifically, the fact that certain results and performance were leaked publicly last year demonstrates that there truly is no confidentiality with these tests. It is not right for a player’s intelligence, aptitude or mental processing to be subject to public discussion and ridicule — no other job interview carries the same scrutiny.

“While our clients are happy to participate in the standard pre-draft physical activities and any football-based interviews or film review, we will not subject them to the wide variety of psychological tests.”

All the concerns over the S2 are not so much to do with the test so much as the leak. Executives still gave the test high marks to The Athletic, with one saying the “science behind it is really sound.”

“It gives you a snapshot of how quickly an individual can process information, and I don’t think there’s a better tool on the market for that. I feel really comfortable with the data we get back from S2,” the exec said. “Is it foolproof? Absolutely not. Nothing’s foolproof. But it does give you a sense of how quickly a player can make split-second decisions.”

S2 scores from active NFL quarterbacksPart of the reason the S2 has garnered so many positive reviews across the NFL has been for its scores matching with talented quarterbacks.

Though not all scores are released publicly unless permission was granted by the athlete, there are some that have become known.

Patrick Mahomes and Josh Allen both reportedly landed somewhere in the mid-90s, and Joe Burrow shared he scored in the 97th percentile. Future Hall of Famer Drew Brees also reportedly landed in the mid-90s, per The Athletic.

Brock Purdy also played a role in helping the test garner some attention, as his score in the mid-90s has been touted as being indicative that the breakout from Mr. Irrelevant could have been predictable. 

Though scores for all quarterbacks weren’t shared, Ally told The Athletic in 2023 that there were 27 quarterbacks tested from 2021 through the 2022 season. Of those, the 13 with a career passer rating above 90 had S2 scores averaging in the 91st percentile. The 14 with a career passer rating below 90 averaged a score in the 51st percentile.