We already knew that the Celtics would likely have to start their postseason run without Irving following a surgical procedure to remove a tension wire in his left patella last month. However, ESPN's Adrian Wojnarowski reported Thursday that Irving will now miss the entire playoffs, a blow to Boston's chances of returning to the Eastern Conference finals.
Relying on their younger talent, the Celtics have managed to go 12-6 in games Irving has missed this season -- a better winning percentage (.667) than any East team save the conference-leading Toronto Raptors. So how well can we expect them to perform in the playoffs? Let's take a look.
Boston offenses suffers without Irving
As you'd expect, taking Irving's efficient 24.4 points per game out of the lineup has a huge impact on the Celtics' offense. In the 18 games he's missed, they've scored 4.1 fewer points per 100 possessions than opponents in those games typically allow -- a rate that would rank 26th in the NBA over the full season.
So without Irving, Boston has relied even more heavily on the league's best defense. The Celtics typically allow 4.8 points per 100 possessions fewer than league average to their opponents. In games Irving has missed, with better defenders replacing him at point guard, that's improved slightly to 5.3 points per 100 possessions better than league average.
Given that Boston's schedule has been a little more difficult than typical with Irving out of the lineup, the sum total is a team 1.6 points per 100 possessions better than average, when adjusted for opponent and game location. But all the Celtics need to do is perform decently on offense to become difficult to beat, even without Irving.
During their six-game winning streak from March 20 through 31, which included wins over Toronto and Oklahoma City and at both Portland and Utah, Boston scored 2.9 points per 100 possessions better than those teams typically allow. If the Celtics can maintain that over the course of a seven-game series, they have a chance to beat anyone in the East.
Who steps forward in Irving's absence?
Let's take a look at how Boston's offense changes shape when Irving sits out. Here's a comparison for the team's top six players in minutes played without Irving, in terms of their share of the offense and efficiency in games Irving has played and those he's missed.
When Irving sits, the Celtics' starting five plays somewhat more equally, with three players -- Terry Rozier, Irving's backup, and starting wings Jaylen Brown and Jayson Tatum -- all finishing between 23 and 24 percent of the team's plays while on the court. (By comparison, Irving has finished more than 31 percent of Boston's plays when he's played.)
Sixth man Marcus Morris takes on a slightly larger role because he's playing many of his minutes with a second unit that lacks scoring punch without Rozier and Marcus Smart, who is currently sidelined after thumb surgery. Fellow reserve Greg Monroe has an even higher usage rate at 27.5 percent of the Celtics' plays.
As is typical, Rozier and Tatum have responded to the increased responsibility by becoming less efficient in terms of their true shooting percentage (TS). But Brown, Al Horford and particularly Morris have bucked that trend. In part, this can probably be traced to Morris getting healthier after dealing with a sore knee early in the season, when Irving was generally in the lineup.
More than that, however, these players have relied on unusually strong 3-point shooting in Irving's absence.
Despite Tatum's downturn (which is probably more regression to the mean than anything else) and the loss of Irving's 40.8 percent 3-point shooting, Boston has shot better as a team on 3s without Irving (38.3 percent) than in games he played (37.6 percent). Naturally, it was even better than that during the recent six-game winning streak: an incredible 48.3 percent. Given the role of luck in 3-point percentages, that raises the sobering possibility that even the 26th-ranked offense the Celtics have played in Irving's absence might not be entirely sustainable in the playoffs.
How far will Boston go?
That concern noted, the Celtics should still be favored to win their first-round matchup. Now all but locked into the second seed after losing Wednesday night in Toronto, Boston should be hoping for the Milwaukee Bucks to finish seventh among the three teams that have a chance to do so. Milwaukee has actually been outscored this season despite a 42-36 record, so the short-handed Celtics have been comfortably better without Irving before accounting for home-court advantage in the series.
While a reasonable case can be made that the Washington Wizards are better than their plus-0.7 differential with a healthy John Wall, none of the three teams Boston could face in the first round (the Miami Heat being the other) have better than a plus-1.0 differential. Factoring in home court, the Celtics deserve to be favored over any of the three teams, even if this series no longer looks like a gimme.
If Boston advances, the conference semifinals present a more difficult matchup. With the Indiana Pacers falling two games back, the third spot in the East looks like a battle between the Cleveland Cavaliers and Philadelphia 76ers, who are currently tied in the standings. Philadelphia's plus-4.0 differential is now better than the Celtics' plus-3.7 mark for the season on the strength of a 12-game Sixers winning streak.
Meanwhile, though Cleveland's plus-0.9 margin would be more at home in the bottom half of the East playoffs, the Cavaliers have outscored opponents by 2.8 points per game since the All-Star break and have a long history of performing better in the postseason than the regular season. Having beaten a Boston team that held home-court advantage (with an All-Star point guard, in that case Isaiah Thomas, dealing with an injury) 4-1 in last year's conference finals, Cleveland is unlikely to be fazed by going on the road.
So assuming whichever team ends up third advances, the Celtics should be considered underdogs in the second round. And while they did beat the Raptors at home without Irving, their 18-point loss Wednesday in Toronto is probably a more reasonable indication of what a potential conference finals matchup between the two teams would look like if Boston were to get that far.
The Celtics' best hope for surviving Irving's injury was for him to be back by the conference semifinals. Now that the possibility is off the table, barring another run of torrid 3-point shooting, Boston's playoff run will probably be shorter than average for a No. 2 seed.