A’s fans of some length of time are used to seeing a slugger wearing the number 25 on his back crushing long home runs at a furious pace for their favorite team. Mark McGwire belted 363 homers during his 12 seasons with Oakland, many of them tape-measure blasts.

McGwire (1996), Scott Brosius (1996) and Jason Giambi (2000) are the only A's players in the last three decades with as high of a batting average, on-base percentage, slugging percentage and home run total through 38 games as the newest No. 25 wearing green and gold, Brent Rooker. The 28-year-old left fielder/DH, whom you probably had never heard of before the past few weeks, is hitting .295/.408/.605 with 11 home runs so far this season.

Who is this guy, and how is he doing this?

Within an eight-month span from April to November of last year, Rooker was in four different organizations. Originally drafted 35th overall out of Mississippi State by the Twins in 2017, he was dealt to the Padres on April 7, 2022, and then traded from San Diego to Kansas City on Aug. 2. The Royals put him on waivers, and the A’s claimed him on Nov. 17.

Generally speaking, someone who bounces around that much in that short a period of time has had some issues with production. But that wasn’t the case with Rooker, who hit at every level of the Minors as he made his way through Minnesota’s farm system.

The trouble was that given the outfield depth in the Twins’ system, Rooker didn’t get much of a chance at the Major League level, and when he did, he didn’t hit. He got even fewer chances at the big league level with San Diego and Kansas City.

Not a problem with the A’s. Now that he’s getting a chance to play every day, Rooker is raking. He spoke with MLB Network’s Mark DeRosa recently on a segment during the MLB Central morning program, and he provided a window into what’s been working so well for him. As you’d expect, what he said checks out with the underlying quality of contact metrics, which we’ll break down here.

Here’s a look at what’s changed to land Rooker on the baseball world’s radar.

He’s playing more

“It’s a tough role,” Rooker told DeRosa when discussing his sporadic Major League playing time before the A’s picked him up off waivers last offseason. Rooker then related a conversation he had with Jon Mabry, who was coaching with the Royals when Rooker was with Kansas City.

Mabry was an outfielder/first baseman in the Majors from 1994-2007. His first five seasons were spent with the Cardinals, and it was the end of his time with St. Louis that he talked about with Rooker.

“I played every day with St. Louis,” Rooker remembered Mabry telling him. “And then we traded for McGwire.”

There’s that big No. 25 again. When the A’s dealt the superstar slugger to St. Louis in 1997, Mabry was the odd man out and moved on to Seattle as a free agent that offseason. With the Mariners, Mabry had to figure out how to perform when he was now primarily being used off the bench and therefore could go days without having an at-bat in a game. He was a part-time player the rest of his career.

Playing time is crucial when it comes to production at the plate, and Rooker is the latest example of what can happen when a hitter gets in the batter’s box during games day after day.

It’s all about the sequencing

Sequencing?

“Your waist is gonna go first [as you begin your swing], then your chest is gonna go, then your arm is gonna go and then your hands are gonna go after that,” Rooker told DeRosa. “So you’re kind of creating that kinematic sequence, allowing you to create the whip and the rotational speed that you’re looking for.”

Getting things in the right order can take you places. In Rooker’s case, it’s taken the baseball deep and over the wall 11 times already this season. Coming into the 2023 campaign, Rooker had 18 barrels, according to Statcast, out of 154 batted balls in play -- that’s an 11.7 percent barrel rate, which isn’t bad.

With his continued sequencing work, Rooker has 18 barrels already this season, for a barrel rate of 19.1 percent. His hard-hit rate is way up, as well, in the top 10 percent among qualified hitters at 52.1 percent.

The idea is to hit the baseball and hit it hard. But also to miss it less, and that’s where his next adjustment comes into play.

He’s chasing less

Rooker’s 22.3 percent chase rate (the percentage of pitches outside the strike zone a hitter swings at) entering play Wednesday ranked in the 82nd percentile among qualified hitters, and was down from 31.4 percent last year.

The result? He’s squaring up the baseball like he’s never done before in the Majors, he’s striking out less (his strikeout rate is 23.6 percent so far this season after he struck out 30.6 percent of the time in 2022) and he’s walking more -- to the tune of 14.6 percent of the time, which places him in the top 10 percent of MLB.

How has he so drastically reduced his chase rate? It has to do with more than the eye can see. And it’s directly connected to his sequencing.

“When I turn and my hands go with me, that’s when the chase comes into play,” Rooker said. “ … If I start my swing for a fastball [with my hands coming with me], and it’s a breaking ball, now I can’t stop, so now I’m gonna chase the breaking ball.

“But if my first move is [to keep my hands back to] create that separation … now I have room to stop back here. … It’s not [just] pitch recognition, it’s just that you’re putting your body in position to have the ability to shut down later.”

The next Big Mac?

Or maybe Mac Junior? OK, enough with the burger puns. Let’s not get ahead of ourselves here. But if you’re wearing No. 25 for the A’s, you’ve got big shoes to fill, and so far, Rooker is  giving us flashbacks to the 1990’s.