The NBA offseason has brought many changes to rosters, coaching staffs, and the list of championship contenders. As we draw closer to opening night, it’s time to move our focus from the potential impact of each offseason event and onto the broader issues that figure to define this season. The BDL 25 takes stock of, uh, 25 key storylines to get you up to speed on where the most fascinating teams, players, and people stand on the brink of 2016-17.

These Boston Celtics are perfectly boring, so Al Horford is a boringly perfect fit.

They are not boring to Boston, because they’re beginning to win, and Boston sure loves its winners.

They’re not boring to the avid basketball fan, either — the X’s and O’s folk — because they’re mistake-free, make the extra pass and maximize every skill on the roster. They’re a well-coached, team-oriented team coached by a swell coach. They’re a basketball coach’s basketball team, whose coach, by the way, doesn’t just live one game at a time; he lives one possession at a time, one practice at a time — maybe even one possession at practice at a time. It is for those reasons that they are boring.

And it is for those reasons Al Horford is perfect for these Boston Celtics. They are a team full of underrated and under-appreciated players in desperate need of a star, so it’s fitting the most underrated and under-appreciated four-time All-Star of his generation chose them in free agency.

“Even though I was with Atlanta last year and we beat the Celtics in the playoffs, I was very impressed with how hard the guys played and how good the team could be under coach [Brad] Stevens,” Horford told reporters gathered at his new team’s Media Day. “What I saw from the group really intrigued me.”

There’s been much discussion about Kevin Durant joining the Warriors after losing to Golden State in the conference finals, but the stranger saga may be Horford joining the Celtics after beating Boston in the first round. This past April, Horford’s Hawks were a year removed from a 60-win season that made them the media darlings of beautiful basketball and resulted in the franchise’s first conference finals appearance since moving to Atlanta in 1968. So, what compels a player to leave the only team he’s ever known to join another that’s seen its season end earlier than his each of the past three years?

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No doubt, the Celtics were good last season, exceptionally good at times. They beat the Cavaliers in Cleveland and the Warriors in Oakland, and yet they’ve won two playoff games in three seasons under Stevens. Probably because their best player was a 5-foot-9 point guard who the Sacramento Kings weren’t even willing to keep. A throw-in to the Rajon Rondo trade and Evan Turner were among the names in the running for their second-best player. This wasn’t your typical up-and-coming roster.

Yet, in each of Stevens’ first three seasons, the Celtics steadily improved in almost every statistical category, most notably offensive rating, defensive rating and wins. A bizarre four-way tiebreaker last season meant the difference between home-court advantage and a road series in the first round.

Come to think of it, in the waning moments of a Game 1 that made all the difference in that series, it was Horford who perfectly executed a pick-and-roll layup to break an 88-88 tie, sandwiched a pair of hustle rebounds around two free throws and blocked an Isaiah Thomas drive to keep the Celtics at bay in a 102-101 home win for the Hawks. Horford was everything the Celtics so desperately needed — a big man who the offense can run through on one end and the defense can run into on the other.

So, the Celtics set about signing him in free agency. While Boston’s historical inability to sign big names on the open market can in part be attributed to the absence of cap space over the years, everyone in the organization concedes Horford’s decision to join the Celtics represents a changing of the tide for a team that had been trying desperately to land stars in its latest rebuilding effort.

For a moment, they even thought Horford’s arrival might tip the scales for Kevin Durant to join him in Boston. Still, they’re pleased with how the summer played out, even if landing one of the biggest names available isn’t as exciting as reeling in the only one that really mattered. But these Celtics aren’t exciting. They’re practical, and they’re boring. And that’s why they make sense for Horford.

They had the No. 3 overall pick this past June, and they’ll have the Brooklyn Nets’ lottery pick each of the next two years. They had enough cap flexibility to sign two max contracts this offseason, and after signing Horford, they’ll still have enough to chase another next offseason. These aren’t things every free agent necessarily considers. Then again, the little things the Celtics sold Horford on aren’t, either.

“We all know the situation of the flexibility and all the future draft picks and all that stuff — that was there — but for me the guys we have here, the group that’s here, is what I felt good about,” said Horford. “And with coach Stevens, playing under his system, I feel like one of my strengths is passing, and I feel like the bigs in this offense handle the ball a lot. That’s something that excited me. Just the thought of putting all those things together, and then being in a place like this — it’s a special place.”

Indeed, the Celtics relied heavily on their bigs on offense, despite an unreliable bunch. Outside of Thomas, the five other regulars on their roster with a usage rate higher than 20 percent all played in the frontcourt. Now, consider Horford had a higher assist percentage (16.7) and lower turnover ratio (7.3) than any member of Boston’s frontcourt playoff rotation last season. And that’s just the start.

The Celtics sorted through a handful of pick-and-roll partners for Thomas, most often defaulting to Jared Sullinger, who ranked 28th among 199 players in possessions as a roll man (165), but just 156th in points per possession (0.87) on those opportunities, per NBA.com/stats. Conversely, Horford had more roll-man possessions (301) than all but three players last season and ranked a respectable 45th with 1.13 points per possession in those situations, representing a significant upgrade for Boston.

We’ll continue with the Sullinger comparison, since it’s his 23.6 minutes departed to Toronto this summer that will make up the bulk of Horford’s playing time. In search of a floor-stretching big, the Celtics for some reason let Sully attempt 101 shots from 3-point range, where he shot just 28.7 percent. He ranked 11th from the bottom among 213 NBA players who attempted at least 100 3’s last season. Meanwhile, Horford shot a more middle-of-the-road 34.4 percent on 256 attempts in his first season taking more than 36 3’s, and the Celtics expect him to improve in Year 2 of that progression.

“I have no idea what his volume of 3-pointers were, but I know as his game continues to be stretched out — and you want to stretch the defense out, you want them to cover more ground, and I think the 3-pointer is a big part of that — he kept up with the game,” said Stevens. “He made sure he changed as the game changed, and ultimately really did a great job of making that transition look easy.”

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And that’s just the offensive end. Defensively, there were 60 players who defended at least five shots per game at the rim, and Horford ranked 30th among them, holding opponents to 49.4 percent at the basket. Sullinger ranked 57th, as foes shot 54.3 percent against him on 5.7 tries at the rim per game.

Incredibly, the Celtics owned a top-five defense sans a dominant big man last season, allowing 100.9 points per 100 possessions. With Horford as their anchor, the Hawks had the league’s second-best defensive rating (98.8), which is what Boston should expect now that Stevens can roll out a lineup with Horford behind All-Defensive-caliber players Avery Bradley, Marcus Smart and Jae Crowder.

There’s more. Quietly, the Celtics have been building a locker room in the mold of their coach — high-motor, high-IQ and high-character. There’s a reason the Celtics brought Tyler Zeller back on an $8 million salary, letting Sullinger leave for $5.6 million. And Horford is perfect to lead such a bunch. The 30-year-old veteran is older than every member of the Celtics, except Gerald Green, and he carries a level of respect matched by few NBA players. The next bad word said about Horford will be the first.

“That’s why we went after him, and we’re not asking anybody who comes in to be outside of their personality; just be yourself to the best of your ability,” Stevens said from the team’s annual Shamrock Foundation charity golf event. “I think his authenticity is one of the things that attracts people to him. He carries himself in a way that screams, ‘I’m here, I’m about the team and it’s about winning.’ We ask that out of all of our guys and hopefully that has a catalytic effect on our team.”

What’s surprising isn’t that the Celtics identified Horford as a perfect fit; it’s that Horford recognized and based his decision on how perfect a fit it actually was. The aging All-Star who prioritizes system and long-term organizational outlook over location and instant championship gratification is a rarity.

“Looking at my career at this point, I’m going into my 10th year, and I want to be able to be a part of something special and win a championship,” said Horford, who’s had a unique vantage point of Boston from Atlanta, facing the last title iteration of the Celtics as a rookie in 2008. “With the type of guys we have here, we have that possibility, and that’s something that I wanted to be a part of.”

Nobody really considers the Celtics legitimate title contenders now, not with the super Warriors out West or LeBron James still dominating the East, even if Las Vegas gave them the fifth-highest over/under for win total (51.5). So, when Horford says “win a championship,” he probably means at some point in his four-year deal, since even he isn’t willing to conceded he completes the puzzle.

When asked if he’s the final piece at Media Day, Horford said, “I’m not sure about that, but I know that I’m going to help our team be better. I’m going to try to come in and jell as fast as I can and just make sure that we’re playing at a high level, that we’re working every day, and we’ll see what happens.”

So boring, so Celtics. While Stevens’ plan of attack continues possession by possession, practice by practice, game by game, team president of basketball operations Danny Ainge will keep adding to his coach’s arsenal piece by piece. Horford isn’t the final piece, but he’s the next piece — one that should help Boston improve from two straight one-and-done playoff series to the second round and beyond.

“We have a long way to go to be considering talking about any of that stuff, and to be quite frank, as I told our team real briefly before we walked out here, there was not a lot of room between finishing 10th and second last year in the East,” said Stevens. “Ultimately, if you want to be the best, or if you want to be among those considered the best, there’s a lot of hard work ahead, and it’s day by day.”

Little about slow progress is exciting. Although, one of those days, perhaps even because of Horford’s arrival, the Celtics might find the final piece to fit into this puzzle of emerging from the NBA middle. And there’s nothing ever boring about having the Celtics back in legit championship contention again.

Previously, on BDL 25:

Chris Bosh’s increasingly hazy career prospects

Kevin Durant sets about winning back our love

Stephen Curry’s search for an encore, and for invincibility lost

The NBA, social activism and a change we need to see in 2016-17

The Trail Blazers, and the promise and peril of ‘pretty good’

Will the Pistons ever get into gear?

Introducing the (maybe) thoroughly modern Grizzlies

Is the new-look Indiana Pacers core worth fearing?

It’s time for Anthony Davis to resume blowing our minds

How will the Warriors recover from a historic Finals collapse?

Counting on the Clippers to contend is insane, so call them crazy

The 76ers and the fascinating challenge of figuring it all out

On the final ‘couple of years’ of Dirk Nowitzki in the NBA

Can Jimmy Butler and ‘the three alphas’ coexist on the Bulls?

The Knicks make no sense, which makes all the sense in the world

LeBron, the Cavs, and writing sequels to storybook endings

Russell Westbrook is going to absolutely go nuts this year

The Spurs’ post-Duncan challenge of winning the West

The Lakers venture into the post-Kobe era

Expect the Utah Jazz to take a big leap forward

The Rockets try to regain a sense of decency

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Ben Rohrbach

is a contributor for Ball Don’t Lie and Shutdown Corner on Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach