BRADENTON, Fla. -- In the words of Cole Tucker, Mitch Keller was the offseason's “internet sweetheart.” For good reason.

In the midst of the lockout, Keller set social media ablaze. With the content machine abnormally quiet, a video of a Keller bullpen session made the rounds across the world wide web. The collective reaction was bewilderment.

His fastballs were sharp, mean. His breaking pitches were sharp. In-person observers were befuddled. Those observing through phones were equally tantalized.

“It was probably the one time I’ve been [a] really big fan of social media, with the fact you could actually see video of guys that were putting it out,” said manager Derek Shelton.

Keller’s viral bullpen session was conducted at Tread Athletics, a private training facility that was introduced to him by former Pirate Clay Holmes. There, Keller had one main goal: re-lengthen his arm action.

Keller had shortened his arm action beginning in 2020. Devin Hayes, a performance coordinator at Tread Athletics who worked extensively with Keller, explained that shorter arm action essentially took away velocity and Keller’s ability to “supinate,” or turn his wrist. The numbers are jarring.

Before Keller shortened his arm action, his average fastball velocity was 95.4 mph. The last two seasons, Keller’s fastball velocity dropped below 94 mph. By re-extending his arm action, Keller would more effectively supinate and utilize his body’s upper half. Those tweaks, in turn, would lead to better stuff -- better results.

To achieve that length, Keller frequently performed a figure eight drill to help create fluidity and improve arm path. Keller also did the “Kikuchi Drill,” named after Yusei Kikuchi, which helps with the body’s lower half. To complement all the throwing, Keller went through general strength and conditioning during his week with Tread. Social media soon discovered the fruit of Keller’s labor.

“He’s awesome," Keller said of Hayes. "I love working with him. He’s such a great dude. He’s helped me tremendously.”

At week’s beginning, Keller threw the first of two planned bullpens. In his first, Keller sat between 95-98 mph per Hayes, who called it “ridiculous.” After a week of work, it was time for Keller to let it eat once more. According to Jamie Johnson, a player development coach with the Mariners who caught the viral bullpen, Keller touched as high as 102 mph, the fastest pitch Johnson had ever caught. More than 630,000 Instagram views later, Keller did, indeed, become something of a social media darling.

“That was probably the most electric bullpen that I’ve ever caught,” Johnson said. “There were so many people in there watching him. ... That bullpen, specifically, is something I will always remember.”

“I didn’t really expect that to get the reach that it got,” Hayes said. “That’s one of the coolest things I’ve ever seen in person.”

The raw data was as tantalizing as the visuals. Per Hayes, Tread Athletics’ database revealed that Keller has four “plus” pitches in terms of movement, spin and velocity. Based on the data from his second bullpen, Keller’s comparison was Gerrit Cole. Some of Keller’s pitches even graded out better than Cole. Keller enjoyed seeing his name next to one of the game’s finest, but understands that turning those outliers into averages is what matters most.

“It’s cool to see the comps, but with comps like that, that’s exactly what it is: a comparison,” Keller said. “To line those up with him, it’s really cool, but consistency is the key there. He brings consistency every single day with those types of numbers. That’s what I'm striving to get to.”

Keller, who revealed that he is working on incorporating a slurve, has flashed top-of-the-rotation stuff, but he has yet to put it all together. His career ERA stands at 6.02 across 39 starts. Before exiting his first Spring Training start on Saturday after getting hit in the thigh by a line drive, though, Keller was phenomenal.

His average fastball was 96.7 mph, nearly three ticks faster than last year. To Shelton, Keller's ability to command his stuff was just as impressive. In 1 2/3 scoreless innings, Keller looked like a staff ace.

Keller knows he can be better. He wants to be the Opening Day starter: “I’d be lying if I said I wasn’t,” he admitted. Should his offseason work translate to in-season success, Keller might have himself a few more viral moments.

“I believe in myself wholeheartedly that I can be the best pitcher in this organization, in the league and the big leagues someday,” Keller said. “I know I have that in me. I just have to go out there and do it now.”