PEORIA, Ariz. -- Those who intently read scouting reports and prospect rankings by now know all about George Kirby’s velocity spike into the high-90s, the deceiving arm speed that he sells his offspeed pitches with and, of course, the pinpoint command that has yielded among the lowest walk rates in the Minors.

Yet he hasn’t always possessed that precision. In fact, his biggest pitching weapon in youth was an all-over-the-place offering that has slowly receded from the pro ranks: the knuckleball.

“It wasn't commanding in the strike zone well, but people were swinging and missing because I threw hard at that age and no one had ever seen a knuckleball before,” Kirby said at the Mariners’ Spring Training facility, where the Minor Leaguers opened camp last week.

No, he doesn’t use the knuckler in-game anymore -- but that doesn’t mean he couldn’t if he wanted to.

“Absolutely,” Kirby said. “It’s nasty.”

The confidence with which Kirby spoke of his favorite pitch of yesteryear was emblematic of his approach to the 2022 season, one in which he will, barring the unforeseen, make the Major League leap. Seattle’s No. 3 prospect per MLB Pipeline and baseball’s No. 33 overall, Kirby has checked every player development box since being taken with the No. 20 overall pick in the 2019 Draft, and he is widely viewed as one of the more advanced pitching prospects in the game.

A “quiet assassin” of sorts, as referred to by scouts and teammates, Kirby embodies that persona well beyond the mound.

“I've never been scared to face anyone older than me,” Kirby said. “My plan is always just attacking the zone and seeing if they can beat me. I've been doing that for years and it's working out pretty good.”

“When you're talking to George right here, he's laid back, chill, really relaxed,” said fellow pitching prospect Isaiah Campbell. “But the golf course, when he gets on the mound, he's a competitor -- a different animal.”

Kirby is coming off a 2021 in which he climbed from High-A Everett to Double-A Arkansas at midseason and reached 67 2/3 innings over 15 starts, an accumulation that would’ve been higher had he not experienced right shoulder fatigue in July. Yet when healthy, Kirby continued to wow, compiling a 2.53 ERA and striking out 80 for a 29.1% rate. His walk numbers remained among the best in the Minors; just 15 to 274 batters (5.5%).

What the Mariners have been most impressed with is Kirby’s ability to maintain his elite command while experiencing a significant increase in velocity. When the club drafted him out of Elon University, Kirby was sitting at 92-93 mph and topping out at 95. Last season, the right-hander averaged 96 mph and was touching 100.

“I think just the older I get, I throw a little harder,” Kirby said. “I definitely put a lot of work in my body just trying to get really healthy. The velo has come and it hasn't hindered my ability to throw strikes either, which is a great feeling.”

He complements the heater with a curveball and a slider, both plus pitches, and a changeup that he’s deliberately turning to more this spring. All of them are lighting up green on the Mariners’ pitch-tracking tools.

“It’s going to be a big weapon for me this year,” Kirby said of his changeup. “I've been just trying to throw it as much as I can; catch play, throw in all different kinds of counts during bullpens and live BP, so it's just been feeling really good. I’m trying to look for 2:30, 3 o’clock spin direction, something that just dives off the plate, and I think I did a pretty good job of that. I’ve just got to make it believable in the zone first, and that way, I'll get a lot more whiffs on it.”

Kirby will be the headliner of the next wave of talent in the Mariners’ pitching-heavy farm system, which was most recently ranked No. 2 in baseball, per MLB Pipeline. The club won’t rule out his shot at the Opening Day rotation, but it seems more likely that it won’t throw him in the ringer right away. Logic suggests that Kirby will begin the year at Double-A, given that’s where he left off and that spring weather can be fickle at Triple-A Tacoma, which could impact his innings-allocation schedule.

Kirby has never thrown more than the 90 1/3 innings during his sophomore year at Elon in 2018, but a leap to the 120-130 range, barring health, could be a realistic target for ‘22. Yet delicately managing those while keeping Kirby on the mound deep into September will be the most vital component to his player plan. Because the Mariners intend to compete for the postseason this year -- and they plan on Kirby being a big part of it.