Feb 27, 2015; Boston, MA, USA; Boston Celtics guard Isaiah Thomas (4) celebrates after making a three point shot during the second half of the Boston Celtics 106-98 win over the Charlotte Hornets at TD Garden. Mandatory Credit: Winslow Townson-USA TODAY Sports

Isaiah Thomas only played 21 games for the Boston Celtics this season.

But what a glorious 21 games it was. The diminutive point guard averaged more than 19 points and 5.4 assists in a Celtics uniform. He provided a crucial offensive spark and a go-to scorer for a team which had lacked one for most of the season. And he finished second in voting for the NBA Sixth Man of the Year.

Isaiah’s contributions were not just on the court. The Celtics this season have been a tough squad that will fight everyone, and Isaiah bought into it. After leaving Sacramento and having a tough 46 games in Phoenix, Isaiah became a feisty competitor that backed down from no one.

Sometimes, this backfired–like when he got ejected in his Celtics debut against the Los Angeles Lakers. But Isaiah Thomas has been overlooked throughout his career. And he brought that underdog spirit to the Celtics and propelled them into that improbable push for the playoffs.

Let us rewind back to the beginning of the season. The Sacramento Kings, who had drafted Isaiah with the 60th pick in the draft, chose to go with Darren Collison over Isaiah. It was possible that this was because Isaiah did not get along with Kings star DeMarcus Cousins.

Isaiah signed a four-year, $28 million contract with the Suns, and Phoenix president of basketball operations Lon Babby declared that Isaiah “will quickly become a fan favorite.”

But people outside the Suns organization were skeptical. Phoenix already had two very good point guards in Eric Bledsoe and Goran Dragic. All three guards needed to have the ball, none of them were big enough to consistently defend shooting guards, and none of them were terrific three-point shooters. How was this supposed to work?

It didn’t. As Thomas later told the Boston Globe, “Somebody ended up upset every night.”

The Suns began to stumble around February, and Goran Dragic demanded a trade. The Suns tried to trade Thomas instead, hoping that removing one of the three point guards would make Dragic happy. On Feb. 19, the Suns traded Thomas to the Celtics. They also ended up losing Dragic anyways, who would go to the Miami Heat.

It had been a rough stretch for Thomas, who declared that he was “a team player,” in contrast to Dragic, after the trade. Now that he was with a team that appreciated him, Thomas took advantage and led the Celtics to new heights.

So, in what ways has Isaiah helped the Celtics? It is not enough to just point out his volume scoring ability. After all, anyone can score a lot of points if you give them enough shots.

But there were things Isaiah did that no one else on the Celtics could. First was his ability to draw free throws. Boston ranked just 27th in free throw attempts this season. Avery Bradley and Evan Turner, the two Celtics with the greatest minutes played this season, both averaged less than two free throw attempts per game.

Isaiah by contrast took 6.5 FTA a game as a Celtic. He had a free throw attempt rating of .481, by far the highest on the Celtics. This ability to draw fouls, combined with his acceptable 34 percent three-point shooting, meant that Thomas was an efficient scorer who the Celtics could dump the ball to.

Thomas’s ability to draw fouls and score continued in the postseason. While he only shot 33 percent from the field and 17 percent from three-point range, he compensated by drawing more fouls than ever before. Thomas finished with a .514 TS% against Cleveland. It is not a great number, but he fought hard in the first playoffs of his career.

And while Thomas is a score-first point guard, he did provide passing on a Celtics team which needed one since Rajon Rondo’s departure. Thomas averaged 5.4 assists in 26 minutes per game, and had the highest assist per minute rate on the Celtics.

So, what will Isaiah’s role with the Celtics be next season? That remains a bit unclear. Isaiah had no qualms with coming off the bench this season, but he would prefer to be a starter just like every NBA player. This is especially so since he is Boston’s best player right now.

But Boston would rather see rookie point guard Marcus Smart develop. If Smart struggles, will the Celtics move Isaiah to the starting lineup? And if Smart succeeds, will the two point guards work together better than the three point guard disaster in Phoenix?

These are questions for next season. For now, the Celtics can celebrate everything they managed to accomplish this year. And Isaiah Thomas can celebrate a season that after so much chaos in Phoenix, has ended with a resounding finish in Boston.