I had the same offensive coordinator during my first four NFL seasons with the Patriots. But after leaving Josh McDaniels and New England in 2009, I had a new play-caller almost every year -- and sometimes two in the same season.
There was Chan Gailey and Todd Haley during the 2009 season in Kansas City. From there we went to Charlie Weis, then Bill Muir, then Jim Zorn, then Brian Daboll.
Then I went to Minnesota to work with Bill Musgrave, followed by Norv Turner. In Buffalo, I had Greg Roman. Then I moved to Dallas and had Scott Linehan. I had Terry Robiskie for two years in Tennessee, and then finally I was with Jim Bob Cooter in Detroit.
So, I know a thing or two about adjusting to new coordinators. It isn't easy.
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Even if you're not changing the offensive system, you still have to adapt to a different personality. Every coach is different in how they teach the game, and it takes time for a quarterback to develop trust with their coordinator while learning what they're trying to accomplish on each play.
It's even more difficult for today's quarterbacks to adjust to a new play-caller, because there's less time on task. The offseason is shorter, and the new collective bargaining agreement limits the amount of time players can be in the building during that time.
That means you don't have as much time to absorb a new playbook before you hit the ground running in training camp.
Play-calling continuity matters
I was fortunate in New England: By the time I took the field as a starter in my fourth season, I had been exposed to so much in this offense. I had watched Tom Brady execute it and seen all of the details that go into successfully running the offense.
I had a comfort level with McDaniels, and there was a trust factor between us that I could audible at the line of scrimmage to get into a better play based on the defense's front.
We were on the same page conceptually, and I think that's why a lot of the quarterbacks who have had the most successful careers are guys who enjoyed longevity in the same system with the same offensive coordinator.
"Fighting the system"
For a young QB like Mac Jones, it's more challenging. He had a lot of success as a rookie with McDaniels, but when you get a new coordinator, they might do things differently. They might tweak the protection scheme or how you call something, which sometimes leads to a tendency to "fight the system."
You're learned the offense a certain way and now it's being taught differently, so that can make you stop and say, "Wait a second, we didn't do it this way. Why aren't we doing it that way?" It can cause you to second-guess, because you may have had a recipe for success that you know is proven, so why change that recipe to do things a different way?
As I matured, I learned that there are different offensive philosophies and different ways to teach the game. But you have to overcome yourself at times and make a point to be open-minded. If you continue to fight the system and get frustrated, that becomes mentally taxing, and then you're not at your best. You're worried about other things other than trying to execute that one play, even if it's not the perfect play.
When you embrace the new system and understand there are different ways to have success -- that's when you can really start to grow as a quarterback, because growth only happens when there's acceptance.
Bill O'Brien's unique coaching style
I love Billy O'Brien. We had a great relationship when I was with the Patriots and he was the wide receivers coach in 2008. He's a guy who pulls no punches -- he's going to hold you accountable, and he's going to coach you to a certain standard with a certain level of expectation.
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That's what I loved about him. Occasionally he'd get into a "war of words" with guys, but that was part of how he did it, and he got the most out of his players. I'd always joke with him because he would love going back and forth with me, so we had a great relationship.
I have a lot of respect for Coach O'Brien based on what he's achieved in New England as offensive coordinator, in Houston as the Texans' head coach and now at Alabama as their OC. He has a tremendous amount of experience coaching at all levels.
Why O'Brien and Mac Jones could be a good fit
Mac Jones is clearly a competitor, and he's said he wants to be "coached harder." Well, O'Brien worked with probably the most competitive quarterback I've ever been around in Tom Brady. There were times where O'Brien and Brady got into it on the sideline, where Brady showed his passion and O'Brien wasn't afraid to give it right back.
But at the end of the day, the role of any coach is to push you to become the best version of yourself. And if Bill O'Brien can come in and achieve that -- not just with Mac Jones, but with the entire offense -- then that would obviously be a great thing.
You never know how a plan goes until a coach walks into the building, and there are still plenty of unknowns. But it seems like O'Brien's coaching style potentially could mesh well with Jones and his competitive nature.
Editor's Note: Matt Cassel played 14 years in the NFL as a quarterback, including four with the Patriots from 2005 to 2008. He serves as an analyst for NBC Sports Boston, appearing on Pre/Postgame Live, as a guest on Tom Curran's Patriots Talk Podcast every Thursday, and as a columnist each week during the season.