Up until his injury, the Hawks had the league's 10th-most efficient offense, averaging 104.7 points per 100 possessions. That offensive efficiency often covered for inconsistent defensive performances and had them firmly entrenched at the top of the Eastern Conference's second tier.
But since Horford's season was ended by surgery to repair the torn muscle, the Hawks have been scoring just 98.9 points per 100 possessions, a mark that would rank 23rd in the league across the entire season.
It may come as a surprise to some that Horford was such an integral part of the Hawks offense. He's not a dominating individual scorer or shot creator, and his most distinctive offensive contribution is the mid-range jump shot out of the pick-and-roll.
But what Horford lacks in offensive flash and volume is more than made up for by his efficiency and subtle ability to bend a defense with his presence.
Although they put on a brave face after the news, the Hawks front office clearly knew their entire season had changed:
“We will work with Al and complete our due diligence to determine the next best steps for him,” Hawks president Danny Ferry said in a statement last week. “Injuries are part of the challenge of an NBA season.”
The Hawks came into the season with plenty of frontcourt depth, but as Kris Willis pointed out at Peachtree Hoops, covering for Horford's skill set was going to be a patchwork effort.
In layman's terms there is no replacing Al Horford for the Hawks but they will attempt to apply the best band aid available. Expect to see Coach Budenholzer experiment and tinker with his lineups and rotations over the next few games to see where the pieces fit.
The problem is not so much replacing Horford's numbers as it is the cascading effect, in both rotations and on-court execution, which makes things more difficult for everyone else.
One of the biggest victims of this has been Paul Millsap.
Before the injury, Millsap was using 24.4 percent of the Hawks' offensive possessions when he was on the floor, shooting 46.4 percent from the field and 39.6 percent on three-pointers. Since Horford's injury, Millsap's usage percentage has climbed to 28.2 percent, with his shooting percentages falling to 38.2 and 23.1 percent respectively.
Millsap is a very skilled and efficient offensive player, but for most of his career he's had the benefit of playing off another equally skilled big man who helps draw the defense's attention. In Utah it was Al Jefferson, and in Atlanta his offensive responsibilities were made drastically easier by playing alongside Horford.
Millsap is a respectable post scorer and isolation player, but he's especially dangerous off the ball. Here, a post-up by Horford draws the attention of three extra Spurs defenders, allowing Millsap to slip past his man and cut to the basket.
Here, a dangerous pick-and-roll between Jeff Teague and Horford draws the attention of Millsap's man, allowing him to slip back behind the three-point line.
Millsap is adept at making the most of these offensive openings, but the way Horford's skills as a shooter and passer threaten the defense went a long way toward creating these types of shots.
Without Horford, those same openings haven't been as easy to find. Millsap is now either acting as the offensive fulcrum instead of Horford or playing off of teammates who don't draw defensive attention in the same ways.
Here the Hawks are running a side pick-and-roll for Teague and Millsap. Gustavo Ayon is in at center and hovering on the strong-side baseline. If Horford were on the floor, he would likely be stationed near the weak-side elbow. That extra strong-side defender takes away Millsap's option to fade to the corner as he slips the screen, as well as putting an extra body between him and the basket.
Here the Hawks are running another side pick-and-roll with Millsap and Teague. Although he sets the screen from the opposite side of the defender, he ends up slipping the screen and catching the ball in the same place as the last play we looked at.
On this set the floor is spaced better with Elton Brand at the weak-side elbow. However, Brand isn't looking to catch the ball, instead setting a screen with his back turned completely to the play. With no offensive threat out there to deal with, it's an easy decision for Roy Hibbert to leave him and challenge Millsap at the basket.
This tightening of opposing defenses has also really affected Teague.
You can see, from this possession earlier this season against the Sacramento Kings, how having Millsap and Horford on the floor together opened things up for Teague.
Teague and Horford are running a high pick-and-roll with Millsap stationed in the corner. As Teague comes off the screen, Horford pops out to the elbow. Both Horford and Millsap's defenders are too afraid to leave them, and the lane is wide open for Teague.
Compare that possession to this one against the Pacers, with Elton Brand on the floor in place of the injured Horford. Here Millsap is floating on the baseline and Teague is running the pick-and-roll with Brand. Hibbert is already sagging off Brand, who inexplicably pops beyond the three-point line instead of to the elbow. From that position, he's not a threat at all, and no driving lanes are open for Teague.
To be fair, the Pacers play most pick-and-rolls with this strategy. But if it was Horford at the elbow there would be a lot more pressure on Hibbert to be in two places at once or risk having a wing defender sucked into help defense, leaving an open shooter on the perimeter.
While Teague and Millsap may be bearing the brunt of Horford's absence, the effects are trickling down everywhere. Kyle Korver's three-point percentage has dropped from near 50 percent all the way down to 37.8 percent, and his three-point attempts per 36 minutes have come down from 6.4 before Horford's injury to 4.9 since.
The Hawks are lucky enough to be playing in the Eastern Conference, where their hamstrung offense probably won't be enough to pull them out of the playoff race. But playing without him certainly puts the entire organization in stasis.
When we look at the offensive and defensive talents of a player, it's easy to get caught in his individual numbers, losing the intricate ways his production connects with his four teammates. His 18.6 points a game don't seem like an insurmountable loss, but Horford's absence has left a gaping hole in the Hawks' offensive structure.
Statistical support for this story from NBA.com/stats