Isaiah Thomas is doing something this season that we’ve never seen before. With an average of 10.5 points per fourth quarter, he’s on pace to surpass Kobe Bryant (9.5), LeBron James (9.1) and Tracy McGrady (8.6) for the highest fourth-quarter scoring since the NBA began tracking the stat in 1996. He’s also set to end the season as the first player in 20 years to average double digit scoring in a quarter, which is an incredible feat considering Thomas fell to the final pick of the 2011 NBA Draft due to concerns about how his height would translate to the pros.

Thomas has been incredibly efficient in fourth quarters, too. By shooting 48.7 percent from the field, 40.8 percent from the perimeter and 91.1 percent from the free throw line, his true shooting percentage in the final 12 minutes of games (67.3 percent) is better than Rudy Gobert (66.9), DeAndre Jordan (66.3) and Kevin Durant (65.1) on the season. Plus, while his defense has been a major concern, Thomas has been a net positive overall for the Celtics in crunch time.

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At some point during his fourth quarter streak, Thomas’ heroics stopped being a fluke. He is obviously a gifted scorer — players who can pull-up from anywhere on the court and shoot 60 percent around the basket are hard to come by — but it wouldn’t be possible for him to dominate fourth quarters for as long as he has if he didn’t have the right system and teammates around him. As much of a sports cliché as it sounds, they have both played a big role in his success.

With that in mind, let’s take a closer look at how his teammates and coaches have helped him become one of the best fourth-quarter scorers of all time as well as how his approach differs when the Celtics need him most

Floor spacing

The first thing to pay attention to is which players are on the floor with Thomas in fourth quarters. Take a peek at NBA.com, and you’ll see five of the 10 lineups that have played at least 10 minutes in the fourth quarter for the Celtics this season have a net positive. The small-ball lineup of Thomas, Avery Bradley, Marcus Smart, Jae Crowder and Al Horford has surprisingly struggled to stop teams from scoring, whereas the trio of Thomas, Smart and Jonas Jerebko with a center and shooter surrounding them has fared rather well on both offense and defense.

The important takeaway from that data is eight of those 10 lineups are scoring at a similar level as the Rockets, Cavaliers and Warriors. While some lineups have a hard time slowing teams down, being able to stretch the floor for Thomas with at least three 3-point shooters on the court has proven to be incredibly difficult for any defense to stop. As long as the Celtics finish with one of the net positive lineups, their high-octane offense is usually enough to carry them to the finish line.

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Just take a look at the following possession. The Celtics begin the quarter with Thomas, Smart, Terry Rozier, Gerald Green and Kelly Olynyk, each of whom are capable 3-point shooters that are comfortable putting the ball on the floor against closeouts. With the Trail Blazers focused on cutting off lanes to the basket for Thomas, Olynyk makes them pay by popping to the 3-point line when Thomas comes off of the screen.

Now that they’ve established Olynyk as a shooting threat, Thomas can then make Meyers Leonard pay for standing in no man’s land by attacking the basket on the ensuing possession.

The only players who aren’t averaging one 3-point attempt per game for the Celtics this season are Tyler Zeller (0.0), Jordan Mickey (0.1), Demetrius Jackson (0.3) and Amir Johnson (0.8). Furthermore, of the players who are taking at least one 3-pointer per game, all but three are shooting greater than 35 percent from the perimeter: Smart (30.8 percent), Rozier (32.4 percent) and rookie Jaylen Brown (30.4 percent). Even if they aren’t the most accurate of shooters, though, defenses still have to be aware of where they are because they won’t shy away from letting it fly when left open.

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Let’s look at a couple more examples to understand how having a shooting threat at every position makes Thomas’ life much easier. First, notice how Markieff Morris and Jason Smith would rather prevent their assignment from getting an open 3-pointer than helping Trey Burke contain Thomas. It’s a poorly defended sequence by the Wizards, but drawing all five defenders out of the paint means they have to pick their poison.

In the second clip, notice where Kyle Lowry is on defense. Instead of sticking with Rozier on the cut when the Raptors hedge the initial pick-and-roll, Lowry parks himself underneath the basket to stop Thomas from getting a straight-line drive. Patrick Patterson then has to cover two players in the corner, and the Raptors panic when the Celtics start moving the ball around the perimeter following a scramble.

It helps, too, that Boston’s offense doesn’t go down the drain when Thomas doesn’t have the ball in his hands. They’ll sometimes park him in the corner to force his defender to decide between sticking to him like glue or risk helping off him. More often than not they’ll go with the former, which turns the game into 4-on-4 for improved playmakers like Smart to go to work.

While Thomas doesn’t contribute anything to the box score in those cases, it forces the defense to respect his teammates. And when they do, Thomas has proven he can spot-up with the best of them by averaging 1.17 points per spot-up possession this season to rank in the 86.4 percentile.

The perks of being a versatile scorer

There are a couple of ways the Celtics puts Thomas in position to succeed within those lineups, the most obvious being the pick-and-roll.

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Thomas scores around a third of his points on the season out of the pick-and-roll and he ranks in the 94.4 percentile with 1.07 points per possession. Horford is an ideal pick-and-roll partner for him because he’s an excellent screener, and he has the ability to pop or roll depending on the coverage. Simply spreading the floor and running a high pick-and-roll with them is often the best way to get Thomas going because he can pull-up if the opposing big hangs back or take him off the dribble if the defender gets too close.

The Celtics run a lot of side pick-and-rolls with Thomas as the ball handler while overloading the weak side with shooters. It gives Thomas and the roller plenty of space without having to worry about a third defender obstructing his path to the basket.

As we’ve already touched on, Thomas is also comfortable playing without the ball in his hands. He told reporters in January that it’s nearly impossible for defenders to chase him around screens and catch up with him once he’s gained a step on them. It becomes especially useful in fourth quarters when teams begin to load up on him in an attempt to limit his touches because it means they have to account for him at all times.

“It’s hard to double when it’s off ball, especially when you’ve got good guys like Amir, Al and Jonas that set really good screens for you,” Thomas said. “Once I’m running around it’s tough to catch me and guys are just getting me open. I’ve got the easy part of making the play.”

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One of the Celtics’ go-to plays when Thomas doesn’t have the ball in his hands is a double screen on the perimeter. As you can see in the following video, Patrick Beverley gets caught up in Smart’s off-ball screen, leaving James Harden to switch onto Thomas once he receives the hand-off from Crowder. Harden wants nothing to do with guarding Thomas, and Thomas takes advantage by sinking a smooth hook shot over Trevor Ariza when he gets into the paint.

The Celtics run the exact same play on the next possession, only this time Thomas kicks the ball out to a wide open Rozier on the wing. Thomas doesn’t generate many assists in the fourth quarter — more on that later — but he is more than capable of making the right read when teams attempt to take away his scoring.

Doubling Thomas isn’t necessarily the answer, either. Watch as he fights through the double team on the same double screen before passing the ball to Crowder, who then dumps the ball down to Horford in the post with Ariza guarding him. Had Ryan Anderson not doubled Thomas at the point of attack, Horford wouldn’t have had a mismatch in the post.

Another way the Celtics get Thomas open when he doesn’t have the ball in his hands is with a set out of their “Flex Thunder” series. It’s almost what you’d expect to see from Stephen Curry — the Celtics use the threat of Thomas to free up his teammates for scoring opportunities by using him as the screener.

This is a good example of how it works:

DeMarre Carroll gets caught ball-watching, and Corey Joseph is too concerned about Thomas to switch onto Brown on the backdoor cut. Even for someone who isn’t a great passer, it’s an easy lob to make.

There are obviously other options out of it, and it’s here where having versatile wings who are comfortable with their backs to the basket comes into play. Smart continues to improve as a low-post scorer, and Brown is comfortable using his size and athleticism to overwhelm smaller defenders on the block. If either of them can draw a double team in those situations, someone will be open for a 3-pointer.

Neither of those mean anything if Thomas doesn’t know what to do with it, of course, which brings us to the final point..

Thomas’ attitude isn’t something we can measure as easily as his scoring ability or the impact his teammates have on his success, but it explains how he’s been able to sustain this historic run. Earlier in the season Thomas told Mass Live that his teammates count on him to carry them in the fourth quarter, and he can “just go out there without a care in the world.” The latter is somewhat reflective in his quarter-by-quarter scoring breakdown.

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As you can see in the table below (Thomas' stats prior to All-Star Weekend), Thomas’ points and shot attempts in the fourth quarter increase significantly when compared to the first three quarters while his assist numbers decrease. Most importantly, he basically doubles his free throw attempts, which should tell you all you need to know about how he aggressively he looks to score.

Thomas more or less becomes James Harden or Russell Westbrook in the fourth quarter. Not only in terms of production, but in the way he looks to make something happen every time down the court. Mavericks head coach Rick Carlisle said Thomas is a difficult matchup because “he’s got the blue light, which is greener than the green light,” and Pistons head coach Stan Van Gundy echoed similar sentiments by suggesting they should’ve triple teamed him following a loss to the Celtics.

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To get Thomas going in fourth quarters, Stevens often starts him so he can get valuable reps against the opposing team’s second units. Sometimes Thomas will get a breather at the midpoint of the quarter before checking back in for the final stretch, but it’s not unusual for him to play the entire fourth quarter when the game is close. It helps that Stevens does a good job of conserving his minutes during the rest of the game with Thomas ranking 21st in minutes per game (34.5) on the season.

When you put all of those factors together — fresh(er) legs, obvious change in aggression, use of different lineups and different sets — it’s easier to understand how Thomas has developed into a crunch time killer this season. His job isn’t necessarily as easy as he makes it sound, but the combination is at least replicable to the point where he has turned an act into a habit.