Latest in the N.B.A. Injury Crisis: Kemba Walker on a Stretcher

Injuries happen in all professional sports. Players get hurt, even when they are in top physical shape.

But what has happened in the N.B.A. this season has gone far beyond the norm, particularly for the league’s best. Four top-20 players have not seen the court much, if at all, this year. That’s not including the All-Stars who only recently made their debuts, such as Detroit’s Blake Griffin and the Clippers’ Paul George, or other stars who are dealing with day-to-day injuries, like the Nets’ Kyrie Irving and Portland’s Damian Lillard.

On Friday night, Boston’s Kemba Walker was taken off the floor on a stretcher. He ran into one of his own teammates, Semi Ojeleye, and immediately collapsed. Walker received a diagnosis of “concussion-like symptoms,” according to the Celtics, and was taken to a hospital for further evaluation.

And it’s not just injuries to franchise players. Rising young players — likely future All-Stars — are hurt too, such as Sacramento’s Marvin Bagley III and De’Aaron Fox. And, of course, Zion Williamson, the most hyped young player the N.B.A. has seen (or I should say hasn’t seen) since LeBron James, is out till at least next month.

This is unusual, and the injuries are happening as the discussion rages about so-called load management — teams’ sitting players to keep them fresh for the playoffs. The injuries have, it seems, come at the expense of the N.B.A.’s television ratings, and while many injuries are fluky, you have to wonder if teams are going to start resting players for even more games as a precaution.

You could make a new “We Didn’t Start the Fire” with all the names on injury lists. But we’re going to home in on some of the most significant ones.

All figures represent statistics entering Friday’s games.

Golden State’s Stephen Curry is out for several months because of a hand injury, which means he can cheer on the Warriors from the bench, alongside his teammate Klay Thompson, who is out indefinitely with a knee injury. If you have any doubt about Curry’s impact, the Warriors went from a significant playoff threat to the worst team in the N.B.A.

Part of that drop-off comes from losing Kevin Durant, who is now with the Nets — though “with” is perhaps the wrong word. Durant was essentially ruled out for this whole season in the summer because he tore an Achilles’ tendon during the league finals in June. He still signed with the Nets in July.

And then there’s Victor Oladipo, who hurt his knee last January and hasn’t returned to the Indiana Pacers.

The strange thing about the Kings losing Bagley and Fox is that they have done just fine. Bagley has played only one game this season. Fox last played on Nov. 8 against the Atlanta Hawks. Since that game, the Kings have gone 3-1, after starting the season 3-6. The three most recent victories include quality wins against Portland, Boston and Phoenix. The lone loss was by 2 points to the Los Angeles Lakers at the Staples Center, a difficult game for any team to win even at full strength.

Under their new coach, Luke Walton, the Kings finally seem to be rounding into form on the backs of Harrison Barnes, Bogdan Bogdanovic and Buddy Hield. And Bogdanovic comes off the bench! But the energetic Richaun Holmes — a candidate for the All-Chip On The Shoulder Team — has been just as crucial on both ends of the floor, and is on pace for a career year.

Bagley is expected to return soon, while Fox’s return is uncertain. If the Kings can tread water for a while longer, they’ll make the playoffs and be the kind of team no one wants to face.

Last season was a struggle for Gordon Hayward. His return from the prior season’s horrific leg injury did not go as planned. He had trouble getting to the basket, so much of his offense was derived from jump shooting. He didn’t fit next to Irving, and really, neither did the rest of the Boston Celtics.

This season’s Hayward is the All-Star the Celtics signed. In eight games, Hayward averaged 18.9 points, 7.1 rebounds and 4.1 assists. A larger percentage of his shots were coming off drives to the basket. He was finishing 71.1 percent of his shots in the restricted area, compared with 63.9 percent last season. He had more lift, which may have helped with his jump shooting, too; he was a whopping 43.3 percent from deep.

And then he got hurt. Again. Hayward had an operation this month after breaking his left hand during a game against the San Antonio Spurs, and he is sidelined for at least a month. In the grand scheme, this is not a serious injury, but it is surely a frustrating one given the season he was having.

The Celtics aren’t a particularly deep team, and they need his playmaking because of the threats they face in the East from the Milwaukee Bucks and Philadelphia 76ers. Boston has been able to take advantage of a soft schedule, going 4-2 in Hayward’s absence. But the games get tougher now.

The Nets knew Durant was injured when they signed him. He is, after all, an investment in the future. But now Irving and another one of their blue-chip prospects, Caris LeVert, are hurt, as well. This means the team’s three best players are out. Even in a throwaway season, this is a disappointing way to start.

LeVert hurt his thumb this month and had surgery, which is, of course, less distressing than the frightening leg injury that caused him to miss three months last season. He has played 57, 71 and 40 games in his first three N.B.A. seasons. This year, assuming he gets back in a month, he will have missed about 20 games. But he was having an excellent season, on pace for his best. In nine games, LeVert averaged 16.8 points, 5 rebounds and 4 assists. It’s a small sample size, but LeVert’s jump shot is a particular point of improvement. He shot 36.1 percent on 3s in those nine games, compared with 31.2 percent last year.

Irving has a shoulder injury that appears to be day to day. That is not, in itself, a big deal. But like LeVert, Irving has a significant injury history. After starting the season as one of the most dominant players in the league, Irving began slumping before sitting out three straight games, with perhaps more on the way. The Nets have cobbled together two wins without him.

Historically, Irving’s numbers take a dip as the N.B.A. season progresses. If the Nets want to make the playoffs this season, doing so without Irving and LeVert at full strength is going to be exceedingly difficult.

The New Orleans Pelicans are 6-9. They are a winning streak or two away from being in the playoff race, but the injury bug has feasted on them too. Lonzo Ball played in Thursday night’s win, returning from a groin strain that had kept him out since Nov. 8. Brandon Ingram, who is putting up All-Star numbers this season, missed four games with an ankle injury.

There is still about a month or so before Williamson makes his debut, but his addition, assuming that he is healthy, will shake up the race for the playoffs, especially with Ingram back. The bottom half of the Western Conference is very fluid right now. Phoenix is sinking after a hot start, and its starting point guard, Ricky Rubio, is dealing with a back injury.

Williamson will serve, essentially, as one of the most remarkable midseason N.B.A. acquisitions in recent years, and he may elevate the Pelicans to another level.

Portland has its own reinforcement waiting in the wings. The 5-11 Trail Blazers are hoping to get Jusuf Nurkic, one of their best players, back later this season after he fractured his leg in March and missed out on the Blazers’ unexpected run to the Western Conference finals. On Wednesday, Nurkic posted on Twitter that he would not return in 2019.

The return of Nurkic, a talented center, would alleviate some of the pressure on Lillard and C.J. McCollum. To make matters worse, Lillard is currently out with back spasms and has no clear timetable for returning.

For now, the Blazers are relying on the recently signed Carmelo Anthony to pick up the slack. They can still make the playoffs, but 5-11 can turn into 6-18 in a blink, and then the postseason will be out of reach.

Given how this season has gone for the health of N.B.A. players, please, everyone in the league: Get your flu shot. Your teams need you.