Bulls coach Fred Hoiberg tells the media that Isaiah Thomas is "impossible to guard" because the refs allow him to put his hand underneath the ball on every possession. Thomas responds saying "that's not the reason why I'm an impossible cover." (0:49)

CHICAGO -- After watching Boston Celtics guard Isaiah Thomas dominate his team to the tune of 33 points in a 104-95 Game 4 loss Sunday night, the frustration that has been building up inside Bulls coach Fred Hoiberg finally boiled over. Hoiberg believes that Thomas has been carrying the ball at various points through the series and is upset about how the All-Star point guard is being officiated.

"Let me say this, Isaiah Thomas is a hell of a player," Hoiberg said. "An unbelievable competitor -- he's a warrior, everything he's going through right now. He had a hell of a game tonight. But when you're allowed to discontinue your dribble on every possession, he is impossible to guard. He's impossible to guard when you're able to put your hand underneath the ball and take two or three steps and put it back down. It's impossible to guard him in those situations."

Hoiberg said he has been talking to officials throughout the series, telling them that he feels Thomas is carrying the ball. Hoiberg said he has been told by the officials that they would watch for the violation.

The coach was asked specifically when the violation he is asking about -- carrying the ball -- is usually called in the NBA.

"That's a great question," Hoiberg said. "They talk about it every year. They talk about it every year, being a point of emphasis. It should be called. I've said all I'm going to say about it. I'm not going to talk about it anymore."

Celtics coach Brad Stevens said Monday that he isn't concerned with Hoiberg's claims.

"It's not my place to worry about what somebody else is saying. Again, I'm not putting a lot of weight into that," Stevens said. "There's a reason why the best scorers are really hard to guard. In Isaiah's case, it's not any different than some of the other better scorers. He's got a tremendously high skill level, tremendous change-of-pace. He's just a hard guy to guard, he's a hard guy to keep in front of.

"After each and every game all season, and before each and every game, there's a reason why coaches are asked, 'How do you contain [Thomas]? How do you keep Isaiah from doing what he does?' It's just a really hard thing to do."

Led by Thomas, the Celtics knotted the series at two games apiece as it heads back to Boston for Game 5 on Wednesday night.

"Isaiah's a terrific basketball player," Bulls All-Star swingman Jimmy Butler said. "So I wasn't paying attention to whether he was carrying the ball or not. It's not my job to watch that."

Bulls guard Dwyane Wade expressed similar sentiments.

"I'm not getting into the officiating," Wade said.

Bulls coach Fred Hoiberg voiced his frustration Sunday night over how Isaiah Thomas is being officiated, suggesting that the Celtics point guard has gotten away with carrying the ball at various points throughout the first-round playoff series. AP Photo/Charles Rex Arbogast

Wade did acknowledge that he thought Hoiberg's commentary was good for the morale of a Bulls team that has lost two straight games.

"It's great," Wade said of coaches standing up for players in a playoff series. "All players want coaches to have their back. Whenever Coach does that, it makes guys want to do a little bit more for him, want to give him a little bit more. So it's always great when you feel that your coach has your back."

In a separate incident, Butler and Celtics guard Marcus Smart were each assessed technical fouls in the second quarter for exchanging words after Smart had the ball stripped from him by Bulls backup point guard Isaiah Canaan.

"As far as the Marcus Smart situation goes, he's a great actor," Butler said. "Acting tough, that's what he does. But I don't think he's about that. I'm the wrong guy to get in my face. [Smart] needs to take it somewhere else, because I'm not the one for that."

Butler said it was the first time in the entire series that Smart said anything to him.

"First time," Butler said. "Last time too. We're not going to sit there and get in each other's faces like that. He's not about that life, so he needs to calm it down."

ESPN's Chris Forsberg contributed to this report.