Marcus Smart developed this routine during his fourth Celtics preseason.

WALTHAM — Marcus Smart developed this routine during his fourth Celtics preseason.

At least once per game, the 6-foot-4, 220-pound guard looked at the player he was defending, looked at the ball, and ripped it right out of his hands.

Sometimes, it was as quick as a purse snatch. Sometimes, it was a downright mugging with the opposition left on the floor looking around to see what just happened as Smart was feeding a teammate for a basket, while brandishing the smile of a satisfied thief.

“Whenever I decide I want to take it from him,” he said of how often he knows he can pull it off following Saturday’s practice in advance of Tuesday's regular season opener in Cleveland. “Really. If he puts it in front of me, and I decide I want it, I can just take it.

“Just like on offense, with the crossover, or hesitation, or change of pace, you make one guy think you are going one way and you go the other. It’s the same on defense. It’s like a chess game. You give him the impression that he has this lane, and you really know that’s where you want him to go. Because once he goes there you know exactly what to do with him.”

Teammates have used the phrase “winning plays” to describe what Smart contributes for the Celtics.

“That’s why we love Marcus,” Celtics coach Brad Stevens said as he showed the team video of one of the steals early in training camp. “He makes the plays that other players don’t make.”

Or are unwillingly to make. Or don’t feel they have to make.

They are the plays that may show up on the stat sheet as a steal or rebound. But don’t necessarily make you a $20-million-a-year player. As Smart heads into a contract year – with the deadline to sign him to an extension on Monday or he becomes a restricted free agency at season’s end – Smart knows the importance of those types of plays, even as he watches those around the league glide through to major paydays without having to make them.

“If you truly, truly know basketball,” he said, “I’m talking about the guys who actually played and understand that – you know without all those guys who are doing the work, and the little things, for all those guys putting up the numbers, they wouldn’t be able to do it.

“Guess what? Those guys aren’t the guys who are going out there guarding the other team’s best player, then coming back and scoring 40 or 50. Those guys are put on someone who isn’t very much of a threat on the other team. Guys like me are forced to be put on guys who are the best player on the other team. And we take on that responsibility.

“It’s easy to go out go out there and score 40 on somebody. But can you stop somebody from scoring 40? That’s tough.”

It’s a toughness Smart hopes to provide for more extended stretches this season after shedding 25 pounds and reconfiguring his diet. He said he came to the realization that he needed to make a change during last year’s playoff run when he felt himself not always being able to do physically what his mind told him he should be able to do.

“When you can be honest with yourself,” he said, “it really doesn’t matter what anybody else says. I was able to be truthful with myself. I know when I played good. I know when I didn’t play too well. I was my hardest critic. That’s all that matters.”

The changes have allowed Smart to be more explosive getting to the basket, while he said the lighter frame has given him more confidence as a shooter. A career 35.8 percent shooter – including 29.1 percent on 3-pointers – he shot 57.1 percent from the floor during the preseason and was 7-for-12 (58.3 percent) on 3s.

“It takes time,” he said. “Some of these great players we see now, it took them three or four years before they really came into their own. It’s not the first time that a guy had to take a while. It won’t be the last time it takes a guy a while to reach his full potential.”

In what could be a crossroads year in his career – a year in which he either begins to fulfill star promise or becomes typecast as a valuable role player with a ceiling – Smart is shooting for the former, and hoping he will realize that promise in Boston whether the contract extension comes this week or this upcoming summer.

“I know what type of player I am,” he said. “I know I am better than people give me credit for. I am not really worried about it.

“This year is different. It’s a new me. I plan on showing that this year.”

— Scott Souza can be reached at ssouza@wickedlocal.com. Follow him on Twitter @Scott_Souza.