The Boston Celtics came into the season off an Eastern Conference Finals appearance that saw them fall to the Cleveland Cavaliers. Not content with the results, Danny Ainge made some significant moves, starting by trading spots with Philadelphia and using that spot to land Duke forward Jayson Tatum. He followed that by trading Avery Bradley to Dallas, clearing cap space to land Gordon Hayward in free agency from the Utah Jazz. To cap it off, Ainge pulled the trigger for landing a star, sending Isaiah Thomas, along with draft picks, to Cleveland for point guard Kyrie Irving. The C’s looked prime to finally overthrow LeBron James at the top.

When Hayward went down with his broken leg, Boston lost the first two games of the season, and although it was premature to write the season off, the situation looked pretty bleak. Then something happened: they won a game. Then another. And another. With their win on Saturday, Nov. 18 against the Atlanta Hawks, the Celtics have now won 15 in a row.

It’s clear that a healthy Hayward (and Irving and Al Horford for that matter) would be the best thing for this Celtics offense. They currently are 23rd out of 30 teams in terms of team offense at 102 points per game. Their offensive rating sits in 19th. Clearly, this team is not an offensive juggernaut.

So how has Boston been winning all these games? Well, if you can’t score, then you need to stop the other team from scoring, and they have done exactly that. On the season, the C’s have yielded the fewest points against per game at 94. They have the second best simple rating system at 7.84, and have the best defensive rating at 97.2. Teams have struggled from the floor against them, shooting just 31 percent from three-point range.

Tatum and Jaylen Brown have been critical parts of the defense. When they are both on the floor, opponents are shooting 31.5 percent from three, and are averaging 97.5 points per 100 possessions. Add Horford, Irving and Aron Baynes (an unsung hero for this team off the bench) to the mix, that number drops to just over 90.

On a simple game basis, no other game exemplified this stinginess on defense quite like on Thursday, Nov. 16 against Golden State. The Warriors came into this game with the best offense in the league (that fact hasn’t changed), averaging just under 120 points per game. Their big three: Kevin Durant, Steph Curry and Klay Thompson, are all averaging at least 20 points per game. Their lowest point total on the season was 97.

Then they headed to the TD Garden, where neither Curry nor Thompson could get anything to fall, both finishing the game shooting under 30 percent. They couldn’t separate from the tight Celtics defense, and the team finished the night with 88 points, just the fourth time in the last two seasons that they failed to crack 90.

The Celtics are for real, especially on defense. They may not reach 70 wins, but it should not shock anyone if this team breaks through and makes it to the NBA Finals.