During Boston’s conference final-opening loss to Miami on Tuesday night, Marcus Smart stood on the sideline in resortwear, nursing a foot injury and politicking with officials. He did what he could; cameras caught him during a timeout harping on rotations and assignments. But Derrick White, starting in his stead, mustered just 3 points on four shots, and, during the deciding third quarter, the Celtics’ offense stuck to predictable patterns while their defense broke down.

Throughout his career, up to and including his recent Defensive Player of the Year honor, Smart has been praised for the intangibles he brings, and he remains the team’s emotional engine, a glyph of green-haired hustle. But there’s a cap to how much a player in just that role matters, and a key to this season has been his taking on more than what the Tony Allens and Patrick Beverleys of the world do, turning into an opportunistic scorer and a capable floor general. Believing in Smart has always meant putting stock in the small stuff, but as the Celtics have ascended to contender status — and as they look to even their series with the Heat when he returns Thursday night — he’s done enough of the big stuff for it to matter.

Here’s a fitting summary of the evolution Smart has made over his eight years in the league In Game 6 of Boston’s semifinal series win over Milwaukee, Giannis Antetokounmpo brought the ball up in transition, and Smart stood him up at the elbow — an admirable feat in itself for a player giving up 7 inches, 22 pounds and roughly an interstate lane’s worth of wingspan, but hardly a deciding one. Antetokounmpo flicked the ball out to the perimeter and posted up for the possession’s Part 2. Again, Smart took a canny angle, this one shading slightly upcourt against a right-handed drive. He braced himself and brick-walled. The two-time MVP retreated to a fadeaway, Smart shot a hand into his sightline, and the jumper fell short. An outlet pass later, Smart was doing a deft little sidestep to the rim and dropping a left-handed layup off the window.

The handwringing over whether Smart really is the best or most meaningful defender in the NBA has lately obscured the uncommonness of what he brings on that end. It is true that he falls short of the highest tier in certain metrics. FiveThirtyEight’s RAPTOR had him as the 10th-most-effective defender among guards this regular season, looking up at, among others, his teammate White. Defensive win shares landed him fourth on his own team, behind Jayson Tatum, Jaylen Brown and Robert Williams III.

Still, the question of his credentials amounts to whether he is a generational stopper — worthy of becoming the only the second guard⁹ to take home DPOY hardware — or merely an excellent one. Smart is a pass-tipping, dribble-hounding montage, the rare player who can chase sharpshooters through obstacle-course screens and bang with bigs on the block. He weighs more than Jayson Tatum (who is 4 inches taller) and studies Muay Thai to stay on his toes. His 2.7 deflections per game over the postseason and 6 charges drawn — the former number tied for ninth among playoff participants, the latter tops — get at the shape of his influence but fall well short of describing its extent. Over the regular season, Boston featured three lineups that held opponents to less than a point per possession; Smart belonged to all of them.

By the kindest reading (and the one the Celtics themselves subscribe to), Smart brings definitional versatility and ineffable leadership to the league’s best defense, the discipline to attach himself to scorers and the creativity to see and communicate what’s coming several steps ahead. “The recognition piece comes a little bit more because of the team success, and him being the head of the snake as far as that,” Boston coach Ime Udoka said. Even from a less charitable vantage, though, he’s the hardest-to-source cog of the game’s most effective offense-suppressing machine. In the first round of the playoffs, over 132 halfcourt matchups against Kyrie Irving, Smart held the mercurial scorer to an abysmal 38.6 effective field-goal percentage, according to data from Second Spectrum. In the second, when he matched up with Antetokounmpo, the two-time MVP managed 42.1 percent. Here Smart is hounding Irving into a desperation fadeaway …

… and, two weeks later, stepping out of a portal to draw an offensive foul on Antetokounmpo.

Save for the honors he’s getting, none of this is particularly new; when Smart was on the floor his rookie season, back in 2014-15, Boston allowed 1.8 fewer points per 100 possessions than when he was off and goosed its turnover rate by 1.9 percent. But a defense-only initiator is an albatross for a team with title aspirations, and for long stretches of his career, he had verged on that territory. Prior to this season, he managed to shoot higher than 40 percent from the field just once; in four of his first six years in the league, the Celtics’ offensive efficiency dropped when he played. Though the numbers are hardly world-beating this year — 41.8 percent shooting, 12.1 points and a career-high 5.9 assists per game — they nevertheless show a crucial improvement in Smart’s complementary skill set and add up to a 3.9-point boost to Boston’s offensive rating. Boston’s defensive and spiritual totem is now, on the other end, good enough.

Smart’s most viral offensive sequence from the Bucks series came when he swallowed a dose of his own medicine at the end of Game 5, having his shot blocked and his pocket picked by Jrue Holiday in the final minute. But on either side of this, he was useful. His pick-and-roll game — which in early years ended more than is advisable in high-octane passes hurled off of big men’s kneecaps — now involves stringing out the defense and lasering the ball left-handed to opposite-corner shooters. Prior to this season, Smart generated 0.93 points per possession when he used a ball screen; this year, the number was 1.01.

As a scorer, he’s grown adept at leveraging his strength, shouldering a sliver of advantage open into a scoring window.

The stat lines vacillated from night to night in the Bucks series — 21 points and five three-pointers in Game 6, a 2-of-9 shooting night offset by 10 assists in Game 7 — but resolved nicely: 14 points and 5.7 assists over the series. If those don’t sound like much, set next to Tatum’s 46-point salvo or even Al Horford’s 30-point playoff career high in Game 4, they may well have represented — and may continue to represent — the difference between advancing and going home. Of the four teams still playing, Boston has the lowest playoff offensive efficiency. Its game is Smart’s ethos writ large: Make it hell on the opponent, and get what you can yourself.

It’s been an effective formula, over a postseason that’s seen the Celtics already knock off the defending champs, but it’s also a tricky one built on slim margins for error. Sometimes the deciding factor is a fifth-year superstar unlocking new facets of his talent. Other times, it’s an icon of the franchise, cherished for one thing, getting adequate at another.

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