While baseball's obsession with round numbers runs deep, there's little denying the significance of a 300-strikeout season (even in today's K-friendly climate for pitchers).

Only 19 pitchers in the modern era (since 1900) have reached the 300-K plateau within a single season. Here's a rundown of the hurlers who have accomplished the feat.

SIX 300-K SEASONS

Randy Johnson, LHP
Years: 1993, '98, '99, '00, '01, '02
Few pitchers have ever intimidated on a mound as much as The Big Unit, and once the 6-foot-10 Johnson corralled the wildness that plagued him in Montreal and his first years in Seattle, it was lights out for hitters.

"I told Randy he could be the most dominating pitcher in baseball if he would just work on his game," fellow Hall of Famer Nolan Ryan said in 1992. "He was a lot like me when I was younger. He was just pitching and not doing a lot of thinking."

Whipping his high-90s fastball and biting slider seemingly from first base, Johnson wiped out batter after batter in an astonishing run through a remarkable renaissance in his 30s and early 40s. Seven of the top 10 strikeout-rate seasons by a qualified starter through 2002 belong to Johnson, peaking with his banner '01 campaign in which the 37-year-old struck out 37.4 percent of hitters (still the second-highest rate in a qualified season since 1900) before dominating even further during the D-backs' postseason run. The 1,746 strikeouts Johnson accumulated in a five-year period from 1998-2002 might remain unmatched for a long, long time.

Nolan Ryan, RHP
Years: 1972, '73, '74, '76, '77, '89
Before Johnson came along, it was hard to foresee any pitcher striking out as many hitters over as many years as The Ryan Express. Ryan's trade from the Mets to the Angels in 1972 represents one of the most favorable changes of scenery for any player, as the hard-throwing righty blossomed from a back-of-the-rotation starter in Queens to the preeminent strikeout artist in baseball history.

"I've never been afraid at the plate, but Mr. Ryan makes me uncomfortable," said Hall of Fame slugger Reggie Jackson. "He's the only pitcher who's ever made me consider wearing a helmet with an ear flap."

Ryan averaged one strikeout per each inning of a ballgame, first through ninth, which might be the best stat to show his dogged determination to sit down each and every hitter he faced. He also averaged 10.1 strikeouts per nine from 1972-78 (when the average starter during that time averaged roughly five), and then he averaged 10.6 strikeouts per nine in his age 40-44 seasons at the end of the following decade. That's how one becomes the game's all-time K leader by a wide margin.

THREE 300-K SEASONS

Curt Schilling, RHP
Years: 1997, 1998, 2002
Schilling is baseball's modern leader in strikeout-to-walk ratio among retired pitchers thanks to his innate ability to command the ball. His 33 walks in 2002 represent the fewest of any of the 300-strikeout seasons on this list, and all three of his 300-K campaigns rank within the top 10 of that list.

Schilling notched back-to-back season of 300 punchouts in 1997 and '98 with Philadelphia before joining forces with Johnson in Arizona midway through the 2000 season. Two years later, the pair made the D-backs the first team in modern history to boast two 300-strikeout pitchers in the same rotation.

Sandy Koufax, LHP
Years: 1963, 1965, 1966
"The Left Arm of God" was a completely appropriate nickname in the eyes of Koufax's opponents, as they watched impossibly hard fastballs rain down alongside hissing curveballs from the pitcher's mound. Koufax remains one of the most beloved and revered pitchers in history thanks in large part to his willingness to pitch through pain; he likely would have tallied many more 300-strikeout seasons had chronic arm and shoulder ailments not swayed him to hang up his spikes for good at age 30.

"It was frightening," said Hall of Famer Ernie Banks, who famously stated that Koufax would tip his pitches but batters still couldn't hit them. "He had that tremendous fastball that would rise, and a great curveball that started at the eyes and broke to the ankles. In the end you knew you were going to be embarrassed. You were either going to strike out or foul out."

The lefty peaked with 382 strikeouts in his penultimate 1965 campaign, a Major League record until Ryan did his idol one better in '73. Don Veale, the NL's next-closest strikeout pitcher that year, finished more than 100 punchouts behind.

TWO 300-K SEASONS

Pedro Martinez
Years: 1997, 1999
Martinez's 1999 season has plenty of arguments for the greatest campaign by any modern-day hurler. His 37.5 percent strikeout rate that year is the best by any qualified starter, as is his 11.6 fWAR, while his 1.39 FIP rating in '99 ranks second behind Christy Mathewson (1.29) way back in '08. And this wasn't just the case of a pitcher trying to throw as hard as he could; Martinez walked just 37 hitters the entire year. And don't forget the one game that didn't count: When Martinez punched out five of the six batters he faced in an electric All-Star Game performance at Fenway Park.

"The '99 season, I think, was something different," said Martinez, who paced the American League in wins, ERA and strikeouts that year. "The triple crown as a pitcher, you can't top it. In such a difficult era to play, I would have to say that's the highlight."

Martinez's final season in Montreal wasn't too shabby, either. The Dominican righty led the Majors with a 1.90 ERA and struck out 305 to capture the 1997 NL Cy Young Award -- the first of his celebrated career.

J.R. Richard
Years: 1978, 1979
It's safe to say Richard got the baseball world's attention when he tied a Major League record with 15 strikeouts in his debut against the Giants in September 1971. But Houston's righty really put it all together seven years later, when he placed fourth in the NL Cy Young Award voting with a 3.11 ERA and an MLB-most 303 strikeouts. Richard rode his triple-digit fastball and menacing slider to another strikeout crown (313) in '79, and was poised for more the following year before a blood clot in his neck and subsequent stroke brought his career to an abrupt end at age 30. He remains one of baseball's biggest "what if" aces based on what lay ahead in his unfinished second act.

Sam McDowell
Years: 1965, 1970
McDowell was nicknamed "Sudden Sam" for a reason, as his rocking-chair motion from the left side could lull a hitter to sleep before his fastball got on top of hitters with purpose. Like Ryan, hitters could never really get comfortable in the box against McDowell, who led the Majors in walks on five occasions. But he also racked up five AL strikeout crowns with the Indians, beginning with a breakout 325-strikeout campaign in 1965.

McDowell's punchout prowess inspired Sports Illustrated to feature him on its cover in May 1966 with the headline "Faster than Koufax?" -- and the southpaws' heaters were a legitimate source of debate at the time. Control issues would keep McDowell from reaching that kind of level, but he did top 300 strikeouts once more in a 305-inning season with Cleveland in 1970.

Walter Johnson
Years: 1910, 1912
Johnson's fastball was truly unprecedented when he came on the scene late in 1907, and he used that to his advantage for years to come. Whipping his signature heater from a dropdown delivery, The Big Train racked up a record 12 league strikeout titles in a span of 15 years from 1910-24, peaking with a pair of 300-strikeout campaigns at the beginning. Johnson's 313 strikeouts in '10 were just 130 shy of the Boston Braves' entire pitching staff that season, and his 7.6 strikeouts per nine innings were nearly twice as many as the league average.

"His fastball looked about the size of a watermelon seed," Ty Cobb once said of Johnson, "and it hissed at you as it passed."

Rube Waddell
Years: 1903, 1904
Waddell might be remembered for his off-beat personality as much as his pitching prowess, as he occasionally missed starts while he was out of town on fishing trips, and he walked off the mound in the middle of a game. But when Waddell focused his attention toward the catcher, he could be downright dominant. The southpaw paced the nascent AL in strikeouts six years in a row (and led the Majors in each of those last five seasons), peaking with 349 for the Philadelphia A's in '04. That stood as baseball's single-season record for more than half a century before Koufax surpassed Waddell in '65.

ONE 300-K SEASON

Justin Verlander
Year: 2019
Teammate Gerrit Cole got there first, but Verlander was right behind him. Verlander got his 300-strikeout season in the same start that he joined the 3,000-strikeout club. It was another brilliant start for Verlander, who began the night with 288 strikeouts in 2019 and 2,994 in his career. He got to 3,000 in the fourth inning and 300 in the sixth. In a fun coincidence, Kole Calhoun was Verlander's strikeout victim for both milestones, No. 3,000 and No. 300.

Gerrit Cole
Year: 2019
Cole won the season-long race to 300 with his fellow AL Cy Young Award contender Verlander. He reached the mark in the sixth inning on Sept. 18 against the Rangers. It was the latest sign of Cole¡¯s transformation from his years in Pittsburgh, where he topped out at 202 Ks in 2015. The right-hander racked up 276 upon his 2018 arrival in Houston, and has topped himself in '19. Cole put together four starts of at least 14 Ks on his way to 300, while challenging Pedro Martinez¡¯s 1999 record for single-season strikeout rate. With 198 1/3 innings at the time of his 300th K, Cole was the second-fastest pitcher to reach that mark, behind only Randy Johnson (197 2/3 innings in 2001), according to the Elias Sports Bureau.

Max Scherzer
Year: 2018
Scherzer had already clinched an NL-record fifth consecutive 250-strikeout season when he entered his final start needing 10 K's for his first 300-punchout season. The righty struck out at least one Miami hitter in each of the first six frames, and capped off the performance with a lengthy seventh-inning battle against Marlins left fielder Austin Dean. After 10 pitches, Scherzer got Dean to swing through a slider for strike three, earning a standing ovation from the Nationals Park crowd.

Chris Sale
Year: 2017
Sale surged to the line, fanning the Orioles' Ryan Flaherty for his 13th strikeout in his second-to-last start of the regular season at Camden Yards. That made him the first AL pitcher to reach 300 since Martinez in 1999, and just the second southpaw after Johnson to hit the mark since the designated hitter was introduced in 1973.

"That's special," Sale said of joining Martinez in the Red Sox's 300-K club. "We all know that's about as good a company as you can get. Being here and having that name thrown around is special to me; I don't take it lightly."

Clayton Kershaw
Year: 2015
Kershaw entered his final start of the year needing six strikeouts to reach the 300 plateau, and he was efficient in getting there, reaching the mark within the first 10 Padres he faced. The Dodgers' ace kept his typically stoic resolve as the Dodger Stadium crowd gave a standing ovation, but his teammates were certainly aware of the countdown.

"I know it meant a lot to him, even though he lied and said it didn't," said catcher A.J. Ellis. "I was counting from the first strikeout of the game. I knew what we needed to get to and where his pitch count was at, just hopeful he would execute so those strikeouts would pile up and get to that number."

Mike Scott
Year: 1986
Scott and his split-fingered fastball were so dominant in 1986 that the Mets accused him of scuffing the baseball during the NL Championship Series. While that was never proven, Scott's overpowering stuff was undeniable. Scott had never topped 137 strikeouts coming into '86, making his 306 punchouts one of the more unexpected totals in recent history. His 11 starts with 10 or more strikeouts were just shy of half his career total, and his magical '86 also included a no-hitter against the Giants in his second-to-last start.

Steve Carlton
Year: 1972
Cartlon's strikeout reputation was well established by 1972; he had set the single-game record with 19 strikeouts for the Cardinals three years prior. Still, Lefty's 310 K's in his debut season with the Phillies took his career to a new level. Carlton won an MLB-most 27 games and posted a 1.97 ERA for a Phillies club that lost 97 games, making his season the best individual performance by a player on a losing team.

"Sometimes I hit him like I used to hit Koufax," Hall of Famer Willie Stargell once said of Carlton, "and that's like drinking coffee with a fork."

Eight years later, Carlton would help complete Philly's renaissance by winning the decisive Game 6 of the 1980 World Series.

Mickey Lolich
Year: 1971
Lolich's 308 strikeouts in 1971 probably aren't the most memorable achievement of his career -- that would be his three complete-game victories over Bob Gibson and the Cardinals in the '68 World Series -- an indication as to how talented Lolich was in his prime. He worked hard for the honors in '71, leading the Majors with a total of 376 innings that has been topped just one time since. Lolich's 308 punchouts remain a Tigers record, and no Detroit pitcher has equaled his 25 wins from that year since.

Vida Blue
Year: 1971
The A's likely would not have won three straight World Series crowns without Blue in tow, but the lefty's best season came right before Oakland's title run. In his first full season as a Major League hurler, Blue compiled an AL-best 1.82 ERA and a Major League-best eight shutouts to go along with his 301 punchouts, topped that year only by Lolich. Sports Illustrated featured Blue in his day-glo yellow A's uniform in mid-May, labeling him the "hottest" pitcher of them all. With Blue, Rollie Fingers and Catfish Hunter leading the way, the A's punched their first postseason ticket in 40 years, eventually falling to the Orioles in the ALCS.

Bob Feller
Year: 1946
Feller's fastball ranks among the most revered in baseball history, and few could touch it in 1946. In his first full season back from World War II, "Rapid Robert" racked up 348 strikeouts to finish one shy of Waddell's record at the time. Feller tried hard to break the record down the stretch, starting two games on short rest and coming into another game in relief. The Hall of Famer finished with an MLB-most 26 wins, representing about 38 percent of the hapless Indians' total for the season.

Fellow Hall of Famer Bucky Harris, the longtime manager of the Washington Senators, probably summed up the best way to beat Feller: "Go on up there and hit what you see. If you can't see it, come on back."