PHILADELPHIA -- Sixers coach Doc Rivers says he keeps a "catalogue" of video clips showing what he believes to be an unfair whistle against his All-Star defender, Ben Simmons. Rivers wants the league to officiate Simmons correctly, as Philadelphia will rely on Simmons' defense, in part, to dig out of an 0-1 hole in their Eastern Conference semifinals series against Trae Young and the Atlanta Hawks.

"We like Ben on Trae," Rivers told reporters on a video conference call Monday. "Trae, he does a great job of drawing fouls. So, we got to be careful with that. Some, he gets fouled. Some, Trae sells them pretty well. So, listen, if Ben is allowed to guard him, then, yeah, I'm all for it."

The No. 1-seeded Sixers lost the series opener to the No. 5-seeded Hawks 128-124 on Sunday, with Young scoring 35 points, going 11-for-23 from the field and 9-for-9 from the foul line, adding 10 assists.

Rivers said Simmons, who was called for four fouls in Game 1, gets punished because of his sheer size at 6-11, 240 pounds.

"Aggression shouldn't be a foul," Rivers said. "One of the things I've done, I've catalogued those plays all year. So it's not just Trae. In general, how many times Ben has been called for fouls for playing just physical, good defense. Arms are in, he's physical, he's doing nothing [against the rules]. The offense is bumping just as much as the defense.

"I have a list of games where, then the whistle blows. It's almost, 'Wait a minute. That's defense.' So, it is what it is. And you always have to adjust to it. That's one thing I tell our guys. But you should never be penalized for playing straight, solid, legal, physical defense."

Rivers said he thinks the NBA does a "pretty good job" with its officiating overall, but wants Simmons to get a fair shake.

"I don't think you should ever be penalized for being a great defender. Being able to be at 6-10 and get over picks, when a guy is 6-10 or 6-9 and he gets over picks and he gets into the body, it looks physical. But it's legal. And so you should never be penalized for that," he said. "And guards are so clever, they throw their arm back and then it's a foul."

Sixers guard Danny Green, who was Young's primary defender in the first half Sunday when Atlanta pushed ahead by as many as 26 points.

"The tough part as a defender, you want to kind of feel the guy and get into his body when you're going over screens," Green said Monday. "When you're not able to get into his body, because he's obviously going to draw contact, draw fouls, stop, jump backwards or whatever he does to get the foul, you have to play off him more. Which allows him to run more freely.

"So it's tougher for anybody to guard anybody that way."

The Sixers had more success on Young in the second half, holding him to 10 points on 3-for-10 shooting and three turnovers.

Matisse Thybulle acknowledged that Philadelphia can do better against the Hawks' star, but he is no easy opponent to figure out -- with the referees' help or not.

"He's really versatile. He's so quick and his ability to navigate in the paint and make plays for himself and his teammates, it feels like at times you can cut off one thing and he just finds another thing," Thybulle said. "And ultimately, it's just being able to get guys on him to slow him down, bump him off his path. And then as a team, just finishing the plays with rotations and rebounds."