By Brendan Darby, Played briefly in the NFL
It's really f***ing hard. I'm not sure many players memorize it per se; it's more about understanding the concepts rather than just knowing every single individual play call. I'd liken it to learning a new language - it's easier to understand the basic structure of it than it is to memorize the dictionary.
This comes into play when you get to the NFL and move around to different teams (did I mention you're going to get cut? You're GOING to get cut), or have new coaches come in. It's like learning a new language, seeing cognates, and associating them that way (e.g, you've really got the language down when your thought process is "2-Jet means 2-Jet," as opposed to "2 Jet means Slide Right from the last offense I was in").
As far as the Wonderlic - I don't think those scores equate to on-field success. I scored a 31, and I felt like I really struggled to learn the playbook (on a related note, did I mention I didn't last long in the NFL?). On the other hand, there were plenty of guys who didn't score that high who used to ace the "board test," where the coach calls you up to the white board in a meeting to diagram plays against different defenses. I can specifically remember a center with a learning disability who scraped by academically in college and struggled to read books, but was one of the smartest people I've ever seen at reading defenses.;
I don't think it's fair to say a chemist or a programmer, for example, would be better at learning an NFL offense than a security guard. You just need exposure to the sport and the nomenclature/jargon.
And everyone needs to know the playbook, not just four postitions. I've seen plenty of people get cut on the spot for not knowing assignments.
I was in training camp with the Ravens and Niners, and got cut at the end of the preseason with both teams, so those are my thoughts just based on my brief time in the League.
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