Just two years before he began tearing up college basketball, two years before he became the leading scorer on a national championship contender, and two years before he appeared in NBA mock drafts as a potential lottery pick, TJ Leaf could barely walk.

He wasn’t injured in the traditional sense. There was no one play that caused him to hobble, no anguished howl on the court hours earlier. But as he trudged out of the gym, Leaf was in pain.

“After every game, after every practice, it was almost just hard to walk back to the car,” he recalls on a recent Monday afternoon. “Sophomore, junior year, it was terrible.”

In between games during the middle years of his high school career, Leaf sometimes wasn’t even able to practice. He’d sit off to the side with ice bags on both knees. At times, his mind would race, and perhaps even wander toward self-pity. He’d wonder: Why can’t I just be able to go work out? Why can’t I be able to go play pickup right now?

But the same reason he pondered those questions, the same reason the ice was on his knees, the same reason the walks to the car were so arduous is one of the reasons Leaf, now a freshman forward at UCLA, averages 16.8 points, 8.7 rebounds and 2.6 assists per game for the third-ranked Bruins.

At the time, the 6-foot-10, 17-year-old Leaf hadn’t been 6-foot-10 for long.

The growth spurt began in earnest during his freshman year. Leaf, who had played on the wing all his life, sprouted from 6-foot-1 in eighth grade to 6-foot-4 as a high school freshman, and ultimately to 6-foot-10 by his junior year. As he grew and adjusted to his new body, the pain intensified.

“It sucked for a while,” he says matter-of-factly.

Eventually, though, the pain subsided, and finally evaporated. The pre-spurt skills, on the other hand, never did. The passing, the dribbling, the foot speed, the shooting — they’ve carried over from Leaf’s guard days, and have turned him into one of the most versatile, multi-talented players at this level of the sport.

“Now,” he says of the growth spurt, “I wouldn’t trade it for anything.”

And although the development arc sounds unusual, Leaf isn’t alone. As the game trends more and more toward pace-and-space, and as power forwards and centers with guard-like skills become more and more coveted, a striking number of college basketball’s best big men have become invaluable assets to their teams in part because only a few years ago, they weren’t actually that big at all.

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The Creighton athletics weight room is lined with dumbbells and barbells, lifting racks and plates, exercise balls and jump ropes, and everything in between, and it was here, in June of 2015, with sunlight streaming through the windows on one side, that Justin Patton’s Creighton career began. The Bluejays’ athletic performance staff puts every incoming freshman through a variety of tests to gage core strength, hip flexibility, vertical leap and a wide range of other attributes. The results of the tests set a baseline for the years of training to come.

But when Patton, who had measured in at 6-foot-11, 204 pounds, reached the bench press and saw 185 pounds loaded up, ready to be lifted, there was a problem.

Patton couldn’t lift 185.

Head strength coach Dan Bailey recalls having to modify the test because Patton, who turned 18 that month, was so underdeveloped physically.

And he was so underdeveloped physically because three years earlier, he was in the same position as Leaf. He never had the pain Leaf did, but he was in the process of growing seven inches in one offseason, from 6-foot-2 to 6-foot-9 in between his freshman and sophomore seasons of high school.

Patton’s path from 6-foot-2 shooting guard to 7-foot NBA prospect illuminates both the benefits and challenges of such a growth arc. Not only did Patton’s weight and strength not follow his height; not only was he unable to fit into the same pair of clothes for more than a few months; Patton, to some extent, had to re-learn basic skills like running and walking.

“It seems easy,” Patton explains, “but it’s hard when you just grow so tall. Just running down the floor, I was tripping, I’d fall over my feet. Or if I got hit, it’s like a tower got knocked down.”

Others have experienced similar difficulties. Significant growth spurts can affect coordination. Vanderbilt’s Luke Kornet, who grew from 6-foot-2 to 6-foot-10 between his sophomore and senior years of high school and didn’t stop growing until he was 7-foot-1 his sophomore year of college, remembers rolling his ankles a lot. He, like Leaf, had joint pain, and sometimes struggled to lift his legs when trying to run.

When Kornet arrived at Vanderbilt, he couldn’t squat 90 degrees. “It took a while to adjust to my body before I was really able to start getting more athletic and stronger,” he says. But Kornet, now a senior, transformed his body, overcame the side effects of the growth spurt, and now averages over 13 points and 6 rebounds per game on a Commodores team that is charging toward the NCAA tournament bubble. Kornet dropped 21 on Kentucky Tuesday night in a near-upset.

Patton’s body had to undergo a similar transformation. At 204 pounds, “He was not ready to play in a college game,” says Creighton coach Greg McDermott. The former four-star recruit redshirted his first year on campus, and dedicated himself to the lifting regime. “While everyone else had game day,” Bailey says, “Justin’s game day was in the weight room.”

A big part of the transformation was Patton’s diet. “Everyone loves to eat,” he says, “but if I had something else to do, I wouldn’t eat.” Through recovery shakes, protein bars and proper nutrition, Creighton’s dietitians laid out a plan for Patton to take in as many as 6,000 calories per day. In a year-and-a-half, he put on 29 pounds while decreasing his body fat by one percentage point.

Once he did, the skills he had displayed as a middle-schooler in Omaha reemerged in a frighteningly skilled 7-footer as comfortable running a fast break as he is around the basket.

For Patton, the skills “naturally carried over.” Others have experienced a similarly quick re-learning curve. For some, ball handling suffers simply because of the increased distance between hand and court. For others, shooting is hindered. But re-honing the skills is easier than honing them for the first time.

“I attribute my passing skills, and the stuff that you don’t see normal big men do, all to growing up [as a guard], and my dad grinding me out on ball-handling drills,” says Wisconsin’s Ethan Happ, who went from 5-foot-9 in eighth grade to 6-foot-6 in 10th. “Then when I grew, I just maintained that.”

Leaf ascribes his exquisite footwork to his days as a guard too. When he catches and faces up to a defender in the post, “my first step is a lot faster than people realize because I grew up as a guard trying to get past that defender [on the perimeter].”

Says Kansas State’s Dean Wade, who grew from 5-foot-10 in eighth grade to 6-foot-6 his freshman year, and who is the Wildcats’ most efficient offensive player: “I don’t know how, but [the footwork] kind of came natural to me.”

Wisconsin coach Greg Gard, who has helped three guards-turned-big men — Jon Leuer, Frank Kaminsky and now Happ — develop into all-conference talents, says the transition from the perimeter to the post is far more natural than a move in the opposite direction. “A lot of the perimeter skills,” Gard explains, “in terms of footwork, passing, decision making, feel for the game, can be applied to playing with your back to the basket.”

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The results speak for themselves. Of college basketball’s top 20 or so big men, at least six or seven experienced massive growth spurts after growing up as guards. St. Mary’s’ Jock Landale, who was 5-foot-11 at the onset of his freshman year of high school, is second in Ken Pomeroy’s Player of the Year rankings. Leaf is the best scorer on the most efficient offense the sport has seen over the past two decades. Happ is the second best player in the Big Ten, and leads Wisconsin in every major statistical category. Patton could be a lottery pick. Richmond’s T.J. Cline, who jumped from 5-foot-9 as a high school freshman to 6-foot-8 as a senior, ranks 12th nationally in assist rate; he’s the only player in the top 100 taller than 6-foot-6.

The phenomenon extends to the NBA too. All-Star Game MVP Anthony Davis was a 6-foot-3 guard at the beginning of his junior year of high school. Then there are former college stars like Kelly Olynyk, who redshirted as a junior at Gonzaga to conquer the residual physical effects of his high school growth spurt.

With more and more teams now prominently featuring small-ball lineups, stretch-fours, and now even stretch-fives, have become more and more valuable, and thus the unique skill sets engendered by these late growth spurts are more and more useful. “When you have a player like that, much like Kaminsky was, you can really run your offense through them,” Gard says. “Because they’re such good passers, they have a feel for the game, they see the rest of the floor, the game slows down for them.”

All of this begs the question: How do coaches evaluate tall high schoolers who grew up as guards? Are they more intrigued by a late growth spurt? Is it something they even specifically look for?

“Absolutely,” says McDermott, whose son, Doug, was also a late bloomer. “The ability to handle the ball and pass the ball, for a frontline player, is very valuable. And while there are good passing big guys, anybody who grew up handling the ball more, and passing and catching and doing all the things you do out on the perimeter, it’s really gonna help you in the post. So it’s always very intriguing when you have someone who played guard most of their life, and they have a growth spurt and they can use those skills to be effective on different parts of the floor.”

Recruiting, Gard points out, is an inexact science, and even more so when trying to project players who haven’t grown into their bodies. Plenty of players who hit huge growth spurts don’t pan out. Some are plagued by injuries. Others never get over the physicality they meet in the paint.

Gard, despite his program’s success with players like Leuer and Kaminsky, doesn’t go as far as McDermott does. “I would say we’re intrigued by it,” he says. “I wouldn’t say we necessarily go hunt for it. It’s more by accident that this has happened.”

But even if he doesn’t hunt for it, he’s drawn to the type of player that a late growth spurt can spawn. When he and his staff see a player with good size and perimeter skills, they start delving into his background. When they learn of the spurt, everything clicks. “Then what you see,” he says, “what you evaluate, starts to make sense.”