Late in Game 3 of Boston's first-round playoff series at Philadelphia last April, Payton Pritchard felt a tap on his shoulder at the Celtics bench. He turned to find Allen Iverson, dressed in black and wearing a Roman numeral III necklace. According to Pritchard, Iverson told him: "You're the coldest white boy I've ever seen." Pritchard had already hit five 3-pointers that night.

The compliment fit the numbers. Last season, no player in the league posted a better effective field goal percentage on isolation plays than Pritchard, whose 58.6% topped Nikola Jokic (57.1%), Shai Gilgeous-Alexander (56.4%) and Luka Doncic (55.8%). At the midpoint of the 2025-26 season he was averaging 1.30 points per isolation possession, according to Stat Defender, a pace that would have been the best for any player in a decade. He cooled in the second half, but his 1.11 points per possession for the season still ranked third in the league, behind Doncic and Gilgeous-Alexander, per NBA.com.

Moments after Iverson's remark, Pritchard hit a step-back 26-footer as the buzzer sounded. Two days later in Game 4, he made a one-legged buzzer-beating 3 at the end of the first quarter, scored 18 first-half points to the starting five's combined 24, and finished with 32, a career high for both the game and the playoffs. He did it all off the bench, two seasons after winning Sixth Man of the Year. He also started 50 games last season after Jrue Holiday left for Portland and Jayson Tatum suffered a serious Achilles injury.

The source of that production is an offseason routine most players would avoid. In mid-June, Pritchard arrived at 6:45 a.m. at a sweltering high school gym on Cape Cod, one of the unglamorous, un-air-conditioned gyms he prefers. He recruits Division II and III players, international players and hometown friends, paying for their travel, to play relentless one-on-one defense against him. He works through about 150 possessions in close to two hours, roughly three times a week, and if he shoots under 60% on the day, his defenders get a Chipotle meal on him.

Celtics assistant general manager Dave Lewin compared the approach to that of Kyrie Irving, whom he watched play one-on-one at night during his time in Cleveland. "They're obviously different," Lewin said, but they are the two players he has seen use one-on-one play most for skill development.

The habit began in high school. Before his sophomore year, former NBA guard Steve Blake, near the end of a 13-year career, picked Pritchard up three or four times a week to play one-on-one. Pritchard lost every time. "It just destroyed me," he said. He also dribbled weighted balls until his hands needed bandages and did plyometrics on the school track during lunch, inspired by reading about Russell Westbrook's leap between his sophomore and junior years.

The results show up in odd places. Pritchard ranked third among 57 players with at least 200 attempts in the key outside the restricted area, shooting 56%, behind only Jokic and Kevin Durant. He made 86 field goals with four or fewer seconds on the shot clock, 12 more than Durant, and his 51.6% effective field goal percentage on such shots trailed only Jalen Brunson's 51.7% among players with at least 100 attempts, according to ESPN Research. In Game 5 against the Sixers, he knocked Joel Embiid back several feet on a drive. His trainer, Michael Soares, said Pritchard simply knows how to use opponents' momentum against them.

Broadcaster Brian Scalabrine called Pritchard an outlier who works like a "savage," and said he even hounds teammates after practice to play one-on-one. The stakes are rising. Boston lost a Game 7 to Philadelphia after leading the series 3-1, then traded Jaylen Brown to the Sixers in the offseason. If the Celtics want to return to the top of a tougher Eastern Conference, they will need Pritchard to stay just as cold.