As I was researching a Mookie Betts article yesterday, I kept coming across various suggestions that Betts was thriving because of a more swing-happy mindset. Maybe that’s true on some level, but Betts isn’t actually swinging more. He continues to run one of the lowest swing rates in either league. The key for Betts has been pulling the ball in the air. He’s hunted pitches to drive, and he’s driven them as he wanted. There are few better pull hitters in the game.

That being said, while Betts hasn’t turned into anything particularly aggressive, he has given a little push to his in-zone swing rate. He’s cut down on his out-of-zone swing rate. There’s no benefit from swinging at would-be balls. And as for the rest of the Red Sox around him — this has become a different-feeling lineup. The Red Sox, as a team, have changed their approach, bringing to an end a long era of patience.

I know that seems like a weird thing to say about a team with an above-average walk rate. It’s a higher walk rate than the Red Sox had a season ago, so, in that regard, this year’s team might seem more patient. And where last year’s Red Sox had the eighth-lowest rate of swings at pitches out of the zone, well, this year, the Red Sox still have the eighth-lowest rate. The lineup, as a whole, remains disciplined.

But this gets into the difference between patience and discipline. The Red Sox have been disciplined enough to not swing at too many balls. Yet, last year, no team had a lower rate of swings at would-be strikes. This year, only the Orioles have a higher rate of swings at would-be strikes. The Red Sox are showing their discipline by swinging at a greater number of hittable pitches. Call it selective aggression. And this is something Alex Cora was talking about from the start.

The Red Sox were long known as a team that was perfectly happy to try to work the count. And you’ll remember that, 10 or 15 years ago, such an approach was worthy of praise. Working the count drives up pitch counts, and it increases walks, which can be good for OBP. The Red Sox never wanted to let that approach go. And, you know, as recently as 2016, the Red Sox finished with baseball’s highest wRC+. It’s not like it can’t ever work. But if you think about this era we’re in, there’s less benefit than ever from driving up pitch counts, since bullpens are all so good and so deep. And with strikeouts continuing to soar, the only situation worse than having three strikes is having two. You never know how many hittable pitches you might get. So the Red Sox talked about swinging more, and swinging early.

This is where I think you can see something dramatic. To put this plot together, I went to Baseball Savant. Going back to 2008, I figured out the Red Sox’ in-zone swing rates, and out-of-zone swing rates. More than that, though, I focused only on first and second pitches. This might not be perfect, but it gets the idea across. What’s another way to visualize the Red Sox’ increased selective aggression? Here’s how they’ve swung with the count 0-and-0, 0-and-1, or 1-and-0:

There’s barely any movement in the out-of-zone swings. The Red Sox have stayed consistently low, never falling outside of the best ten teams. The other line, though — that’s a change. In these counts in 2018, the Red Sox have an in-zone swing rate of almost 58%. They hadn’t before managed an in-zone swing rate of 48%. Look at these year-to-year MLB rankings. Even though it’s still only the middle of April, it’s very clear that this is a club with a different mindset.

Red Sox rank in early-count Z-Swing%

2008: 27th

27th 2009: 29th

29th 2010: 30th

30th 2011: 27th

27th 2012: 28th

28th 2013: 30th

30th 2014: 30th

30th 2015: 30th

30th 2016: 30th

30th 2017: 30th

30th 2018: 2nd

Five straight seasons of bringing up the rear. Effectively, at least ten straight seasons of bringing up the rear. And now, second place, behind only the Braves. Here’s how all the teams have changed in this statistic between 2017 and 2018:

To a certain extent, the Red Sox just had to catch up to everyone else. But they’ve also passed almost everyone else, trying to attack hittable strikes before the count gets too deep. It might not be surprising to see this taking place, since the team is just hewing to what its new manager has already said, but I find any shift like this to be remarkable. This isn’t a team going from the bottom to the top in something noisy or accidental, like BABIP. This is reflecting something deliberate. The Red Sox wanted this.

On the one hand, it’s hard to say this approach has been successful, just because of the overall results. On the other hand, that might be plenty. In 2017, the more passive Red Sox finished 22nd in wRC+. As I write this, in 2018, they’re tied for first. Some of that, obviously, is just a function of J.D. Martinez. Martinez happens to be the embodiment of this whole phenomenon — Martinez loves to swing aggressively at pitches in the zone. Martinez’s early-count Z-Swing% this year ranks fourth-highest in baseball. But even he has gotten more selectively aggressive. So have Andrew Benintendi, Mookie Betts, Rafael Devers, and Christian Vazquez. There’s less working of the count taking place. Less taking of strikes, for patience’s sake. It would be hard for any Red Sox fan to complain.

Again, in many seasons, the more patient approach worked just fine. The Red Sox have fielded some extremely productive lineups. This looks like it’s going to be a differently-productive lineup, and perhaps one that’s more suitable for the era in which it plays. Driven by J.D. Martinez, this lineup has a new feel to it. Let this be a word of warning to future get-me-over strikes.