The defending champion Toronto Raptors are on the brink of elimination, down 3-2 in their Eastern Conference semifinals series against the Boston Celtics after Boston’s most complete performance of the series.

With Game 6 on Wednesday (6:30 p.m. ET, ESPN), here are three things to know:

A critical injury for the champs

Serge Ibaka was in a walking boot on Tuesday after suffering a left ankle injury in Game 5. As of late Tuesday night, his status for Game 6 was unknown.

“I will see how I wake up [Wednesday], because it’s different,” Ibaka said. “When it happened last night, I felt like I could still play. Then today, this morning, it changed a little bit. So let’s see tomorrow when I wake up.”

Both Nick Nurse (“I think there’s a good chance”) and Fred VanVleet (“I would be surprised if he wasn’t out there”) expressed confidence that Ibaka will be able to play in Game 6, but only time will tell. And the backup center’s presence is critical, given how the Celtics are defending and given Marc Gasol’s shooting issues.

When the Raptors have run high pick-and-roll with their centers, whether the guard has used the screen or rejected it, Ibaka and Gasol have generally been open when they’ve popped to the top of the 3-point arc.

.@sergeibaka says he twisted his ankle in game 5 and is going to see how he feels tomorrow morning to determine his availability for game 6. pic.twitter.com/uJb5pMvbgD

— Cassidy Hubbarth (@CassidyHubbarth) September 8, 2020

“They’re gonna chase the ball with the big a lot,” Nurse said. “[Daniel] Theis is chasing the ball down the lane a lot, which obviously means your big can either roll or pop and get some kick-backs to him.”

Ibaka has been much more willing to take those shots, and he’s 11-for-22 on above-the-break 3s in the series. Gasol, far less willing and far less accurate, is 0-for-10 in about the same number of minutes. He’s been better inside the arc, but had a couple of rough-looking shots at the rim on Monday.

Among 81 players with at least 50 field goal attempts in the playoffs, Ibaka (67.9%) ranks third in effective field goal percentage, while Gasol (43.0%) ranks 78th.

Nurse acknowledged that, whether Ibaka plays or not, his team needs more from its starting center.

“We don’t need a ton,” the coach said. “It’s not like we need 25 from him. But we need him to chip in with some, just because there’s opportunities there for him. As you well know, we need both him and Pascal [Siakam] to provide some offensive punch for us. That’s when we’re at our best, and we need to be at our best to win a game here.”

No breaks for Siakam

Siakam, 75th in effective field-goal percentage (44.4%) among those 81 players with at least 50 postseason field-goal attempts, is another story. The Raptors’ leading scorer in the regular season has averaged just 15.8 points on 41% shooting in this series.

It was noted after Game 1 how much Siakam’s shooting suffers after the first six seconds of the shot clock. In the regular season, he had an effective field goal percentage of 65.7% in the first six seconds of the clock and just 47.4% in the last 18 seconds of the clock, according to Second Spectrum tracking. That differential (18.3%) was the fifth largest among 86 players with at least 100 field-goal attempts in the first six seconds.

Siakam’s 220 shots in the first six seconds were the ninth most in the league and accounted for a little more than 20% of his total field goal attempts. That ratio was about the same (14/71, 19.7%) in the Raptors’ first-round series against Brooklyn.

In this series? Only two of Siakam’s 79 field-goal attempts have come in the first six seconds of the shot clock. And the first of those wasn’t in transition. It was a last-minute, after-timeout iso in Game 2 against Marcus Smart, who stripped him on the way up. (The Raptors were probably looking to iso against Kemba Walker there, but Smart seemingly figured out what they were doing and told Walker to guard OG Anunoby.) The one real transition bucket for Siakam came in the third quarter of Game 4.

So the first answer to “What’s wrong with Pascal Siakam?” is “The Celtics aren’t letting him run.”

Two more issues, which are connected to the lack of transition opportunities, are Siakam’s lack of layups and free throws. In the regular season, 34% of Siakam’s shots came in the restricted area. In the first round, that number was 28% (20/72). And in this series, it’s just 19% (15/79). He’s made 11 (73%) of those 15 shots, but field goal percentage drops dramatically once you get outside of the restricted area, and Siakam has taken almost twice as many shots elsewhere in the paint (11-for-28) as he has in the restricted area.

Tied to that is the lack of trips to the line. In the regular season, Siakam had a free throw rate of 27.4 attempts per 100 shots from the field. In the first round, he upped that to 33.3 per 100. But in this series, Siakam has just 14 free throw attempts with those 79 shots from the field, a rate of 17.7 per 100.

Siakam has shot a reasonable 15-for-33 (45%) with Jaylen Brown defending him, but has just two free-throw attempts to go with those 33 shots from the field. He’s shot 17-for-46 (37%) otherwise.

Siakam saw a big drop in efficiency with his increase in usage this season. And without transition opportunities or free throws, it’s been an even greater struggle for him to provide what the Raptors need offensively.

The impact of Kemba Walker

This has been the ugliest series in these playoffs, with the Celtics and Raptors combining to score just 103.1 points per 100 possessions through five games. But it hasn’t been so ugly on the Celtics end of the floor when Kemba Walker has been in the game.

In 186 minutes with Walker on the floor in this series, the Celtics have scored 112.5 points per 100 possessions. In 54 minutes with him off the floor, they’ve scored just 80.2. Some of that latter number includes garbage time, but even in 45 minutes with Tatum on the floor without Walker, the Celtics have scored just 80 points on 99 possessions.

One big difference has been their shooting. From outside the restricted area, the Celtics have shot 40.1% with Walker on the floor and 30.4% with him off the floor. Walker himself has shot 13-for-19 in between the restricted area and the 3-point line.

The other big difference has been turnovers. With Walker on the floor, the Celtics have committed 13.5 turnovers per 100 possessions, a tick fewer than they averaged in the regular season (13.7). With Walker off the floor, they’ve committed 25.6 turnovers per 100 possessions.

Taking care of the ball has always been one of Walker’s best qualities. The Hornets ranked first or second in turnover percentage in each of his last six seasons in Charlotte. This season, his 8.5 turnovers per 100 possessions used was the sixth lowest rate among 41 players with a usage rate of 25% or higher.

In this series, against the team that ranked second in opponent turnover rate and needs to get out and run, Walker’s ability to take care of the ball is even more critical than usual.

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John Schuhmann is a senior stats analyst for NBA.com. You can e-mail him here, find his archive here and follow him on Twitter.

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