Marcus Smart’s cobra move once earned him a pat on the back from Kevin Garnett. Few receive that seal of approval from one of the fiercest hustlers in NBA history. Smart shares that small space with Garnett’s former teammate Kendrick Perkins.

Sprawling out for any 50/50 ball in the air, on the ground and even after returning from a 19-game absence to thumb surgery, he’ll stick his fingers under heavy bodies on the ground to pry a ball from an opponent’s hands. Much in the same way, Perkins inserted a fear factor into games by absorbing the elbows of opponents like they were plush pillows.

Terry Rozier felt the impact of one of those obscure moments of physicality during Game 5 of the Bucks series. Smart belly-flopped between Giannis Antetokounmpo and Matthew Dellavedova after telegraphing the latter’s pass and running full speed into the ball as it hit Giannis’ hands. He tried the best he could to get it back but landed too late, as Smart rolled the ball toward Rozier for an open three.

Rozier couldn’t believe it. The crowd whipped into a frenzy, as less than one minute following Smart’s entry into a 2-2 series all the momentum landed in the Celtics’ court.

How valuable is Marcus Smart to the Celtics? How badly would the team be hurt if he no longer wears a Boston uniform? Perhaps the man who stood on the sideline with the Cavaliers this postseason is a reminder of how important a defensive anchor can be.

Kendrick Perkins once played a gritty role so instrumental to the Celts’ championship pedigree that news of Danny Ainge’s infamous 2011 trade that sent him out left his locker room in tears. Doc Rivers, famous for his oratory, had few words to encourage his team destined for a second-round exit. Even he knew they’d lose the game on the day it happened.

Perkins’ knee might have been damaged beyond justifying another contract, and the Heat’s big-three talent could have over matched them regardless, but the seed of doubt entered that team’s mind when Perkins exited to the Thunder.

He only averaged seven points and eight rebounds, but as Paul Pierce recalled, “him and Kevin—that was intimidating for teams to play against... Perk snarling at them after blocking a shot, or setting a hard pick on them, or when they come back they know they are going to get hit.

“That was the mental edge that we had on everybody, and it was like we gave that up.”

The differences between Smart and Perkins begin with the fact that the Celtics don’t face the slap-to-the-face of emotion Perkins’ trade hours before a 89-75 loss to the Nuggets placed on the team at midseason. Yet it’s easy to look back at stretches where the team’s defense faltered in Smart’s absence. They went 17-13 in games he missed this past year.

Ainge and ownership will make the final call since Smart is a restricted free agent. The difficult question facing them is: What is Smart worth, statistically and intangibly, to Boston? He is clearly worth more to Boston than he would be to most other teams, but the number is difficult to find. Smart’s camp believes he could earn more than $12-14 million on the open market, per ESPN’s Jackie MacMullan.

Ainge had extended a 4-year, $22 million deal to Perkins, which Oklahoma City eventually topped at $36 million over 4 years. Perkins was 26 years old, and Ainge wouldn’t cross the average annual value line of $9-10 million. Smart’s now 24. Ainge sang a similar tune about this summer, noting that the team would spend to win, but within reason.

There’s no telling what Smart’s market will be until all the figures move into place. The cap, player options and trades will shift available money, but there are few franchises that can currently blow the Cs away with an offer sheet to Smart.

That’s a significant advantage as they narrowly rest below the luxury tax line they’d rather avoid crossing, albeit while returning Smart and free agent Aron Baynes. Every million matters in that sense, especially should there be any gap between what the locker room and front office believe is the ultimate value of a hustle player.

Rivers begrudgingly aligned with Ainge on the Perkins trade, which the front office sold as moving toward perimeter competitiveness against LeBron James by bringing in Jeff Green. He also worried about moving forward with two poor shooters like Perkins and Rajon Rondo causing spacing issues. Mike Zarren showcased splits that held that the Cs fared better offensively in Shaquille O’Neal lineups.

“Sometimes when you’re a GM, you look at talent more than chemistry,” Pierce said reminiscing negatively on Perkins’ departure. “You’re upstairs, you don’t know what’s going on in this locker room... you just kind of see it from afar.”

The details of the shockwaves Perkins’ departure laid on a championship group, detailed in Ian Thomsen’s fantastic new book about the turn of the decade in the NBA, The Soul of Basketball, depict Ainge’s most controversial move to date. People still argue both ways on trading Perkins. Regardless, a source around the Celts as they lost a 108-103 game to the lowly Clippers in the TD Garden while DeAndre Jordan tore through the team’s interior to shoot 9-for-10 remembered a team drooped in spirit as if they were done two months before they actually were.

Even though today’s players would have as long to envision themselves without Smart before they even play a game, Ainge was reportedly ready to pull the trigger on a deal around the timeframe he did with Perkins according to Adrian Wojnarowski. It never formulated, and Ainge later pushed back against the rumor, but it is worth wondering if he learned from the Perkins’s impact beyond his pure physical abilities.

Plenty of players can defend multiple positions, handle the ball in the pick and roll, take charges, play with size at guard and box out. Yet Smart does it with a vigor that catches the attention of his teammates, sends energy through the crowd and even seems to throw opponents out of rhythm.

Every inch, tangible and emotional, matters on the road to a championship. The core of the team would remain intact in the absence of Smart next year, but its heart might be worth a few more million bucks and paying the luxury tax.