Smart had an unusual season from a statistical standpoint in 2018-19. He played in the most games of his career (80), starting a career-high 60 of those, yet he averaged fewer minutes than in either of the prior two seasons. As a result, despite Smart undergoing a major shooting renaissance with a 42.2 field-goal percentage and 36.4 percent three-point percentage -- both easily career highs -- he averaged 8.9 points per game, a four-year personal low, due to a relative lack of offensive opportunities. That said, Smart's superior defensive skills finally gained recognition after he finished third in the NBA with a career-high 143 steals (1.8 per game). That work ultimately got Smart named to the NBA All-Defensive First Team. Smart scored a season-high 21 points three times. In perhaps the best of those efforts, he added seven assists, five steals and two blocks in a Jan. 28 win over the Nets. He posted a double-double Nov. 9 against Utah, notching 13 points and 10 assists. With two games left in the regular season, Smart suffered a thumb injury that required surgery, forcing him to miss most of the playoffs. He returned for the Celtics' final two games of their second-round loss to the Bucks, averaging 1.5 steals despite playing low minutes off the bench.

Injuries derailed Smart's fourth season in the NBA, as he managed to play in only 54 games (11 starts). When healthy, the tenacious guard was again an effective defender (1.3 steals per game), a complementary scorer (10.2 points per game) and a growing distributor (4.8 assists per game, a new career high). Of course, the box score has never accurately portrayed Smart's value to the Celtics. Coach Brad Stevens has come to rely on Smart's ability to defend multiple positions while serving as the primary backup at point guard. On Nov. 27, Smart scored a season-high 23 points in a loss to the Pistons, adding six assists. In late January, Smart suffered a hand abrasion that forced him to miss 11 games. Then, on Mar. 16, he tore a ligament in his right thumb, causing him to miss the rest of the season and four playoff games. Upon his return, though, Smart received plenty of run in the playoffs filling in for the injured Kyrie Irving. In Game 2 of the Celtics' second-round series against Philadelphia, he posted 19 points; he also put up a pair of nine-assist games. All told, Smart averaged 9.8 points, 5.3 assists, 3.7 rebounds and 1.7 steals across 15 playoff games (four starts).

Smart's third NBA season saw him crack a double-digit scoring average for the first time. He put up 10.6 points per game, accompanied by career-high averages in assists (4.6) and steals (1.6), along with 3.9 rebounds per contest. He ranked 12th in the NBA in total thefts with 125. Smart also shot a career-high 81.2 percent from the free-throw line, continuing his trend of improving on that front. Not coincidentally, 2016-17 was the healthiest season of Smart's career, as he appeared in 79 games (24 starts). The Oklahoma State product was the ultimate sixth man for Boston, backing up not only Isaiah Thomas and Avery Bradley in the backcourt, but also Jae Crowder at small forward. Smart double-doubled Nov. 11 against the Knicks with 12 points and 10 assists. Smart notched a season-high 22 points against the Pelicans on Jan. 7, adding five boards, six assists, two steals and a block. On Feb. 15 against the Sixers, he had his biggest game of the year, racking up 21 points and a career-high eight steals along with five rebounds, five assists and a block. Smart appeared in all 18 Boston playoff games during which the Celtics reached the Eastern Conference Finals. For Game 3 in the ECF against the Cavaliers, he replaced an injured Thomas in the starting lineup. He responded with 27 points -- including 7-of-10 shooting from three-point range -- to help garner Boston's only win of that series.

Smart overcame injury to ultimately appear in 61 games in the 2015-16 season. His sophomore season in The Association got off to a bumpy start when he dislocated two fingers on his right hand during Summer League play. The Oklahoma State product then missed 21 games -- including 18 in a row from Nov. 22 to Dec. 27 -- while recovering from a lower-leg injury. However, Smart went on to play in the Celtics' final 52 contests. He provided more scoring (9.1 points per game) and rebounding (4.2 per game) than he had in his rookie season despite starting just 10 times in 61 games after making 38 starts in 2014-15. It helped that he improved his free-throw shooting significantly, upgrading his subpar 64.6 percent rate as a rookie to a more-than-respectable 77.7 percent this time around. Smart also remained a major asset on the defensive end, racking up 1.5 steals per game (good for 26th in the NBA) for the second straight season. On Jan. 15 against Portland, Smart racked up 10 points along with 11 rebounds and 11 assists (both career bests) for his first NBA triple-double. A month and a half later, he notched his first career double-double with 15 points and 11 boards. He also set a new career high for single-game scoring with 26 points, reaching that mark in two separate games.

After being selected sixth in the 2014 NBA Draft out of Oklahoma State, Smart played a significant role for the Celtics as a rookie. He appeared in 67 games, starting 38 times and averaging 7.8 points, 3.3 rebounds, 3.1 assists and 1.5 steals in 27.0 minutes. Smart made an instant impact on the defensive end in particular, recording four steals in his NBA debut Oct. 29 against Brooklyn. He went on to record 27 multi-steal games, nabbing a season-high five on two occasions. Smart also contributed 23 games with double-digit points, clearing the 20-point plateau on two occasions. In his biggest game of the year, Mar. 18 against the Thunder, Smart stuffed the stat line with a season-high 25 points along with nine rebounds, five assists, two steals and two blocks. Though his 36.7 field-goal percentage left room for improvement, Smart shot 33.5 percent from three-point range while averaging 1.4 threes per game. He was named Rookie of the Month in February and ultimately made the All-Rookie Second Team. Come playoff time, Smart started three of the Celtics' four games in their first-round loss to Cleveland, averaging 9.8 points on much-improved 48.3 percent shooting across 22.5 minutes per game.