Everton boss Ronald Koeman said he was "disappointed" by the unfortunate scenes in the stands during his side's 2-0 defeat of Hajduk Split in the first leg of their Europa League qualifying playoff at Goodison Park.
The match had to be halted for a few minutes in the first half when trouble flared in the away section that saw the hosts go in at the interval two goals up thanks to a Michael Keane header and an Idrissa Gueye strike.
It was shortly after Keane's 30th-minute goal that the crowd trouble broke out in the Hajduk section, with missiles being thrown, advertising boards being kicked over and some supporters almost getting on the pitch.
Slovakian referee Ivan Kruzliak called the players off the pitch while stewards and police swiftly moved over to the area en masse, forming a line around the section.
"I was disappointed,'' Koeman said.
"I like to have it really fair, that you can play football, and we needed to stop. I don't know what happened, it was in the corner.''
When Hajduk boss Joan Carrillo was asked about the incident, he was reluctant to comment on it.
"Sorry, but I was concentrating on the game and saw nothing,'' he said.
"I don't want to talk about this.
"I am the coach and I want to talk about the game and my players. These things are not my job.''
Everton were not so dominant in the second half and goalkeeper Jordan Pickford was called upon to make several decent saves to ensure Hajduk did not nick a goal ahead of next Thursday's second leg in Croatia.
Asked how he felt about his team's efforts after the contest, Koeman said: "Really happy about the first half and really unhappy about the second.
"I think we lost a big opportunity to score more goals today and decide qualification.
"We were 2-0 up before half-time, and there was a chance for Wayne [Rooney] to score the third, and then the way how we dropped the tempo in the second half...
"I don't think it's about we were tired after 45 minutes. I don't think our opponent made it more difficult.
"It was us, by ourselves. We dropped the tempo. Hajduk had some good chances to make it 2-1 and we were lucky.
"It is about the tempo of the game and trying to get the maximum out of this game. It is about intensity and the way we need to play, and the second half wasn't good.
"This is two legs, and with a better result it would be even more easy. It will be difficult now.''
Asked if he thought there was an attitude problem, Koeman said: "I don't know, I will ask the players. But it's not how I like to play.''
The Dutchman did single out Pickford for praise, saying: "Maybe there was one on the pitch who played 90 minutes at a high level, and that was Jordan.''
Meanwhile, Koeman has said he remains unsure whether Everton's new record signing Gylfi Sigurdsson will make his debut in Monday's Premier League clash with Manchester City at the Etihad Stadium.
Sigurdsson joined for £45 million from Swansea on Wednesday and was introduced to the Goodison crowd ahead of kick-off.
"We will do some tests on how his physical state is,'' Koeman said. "He told me he did training, played one time 45 minutes in a friendly, and he needs game time.
"If it's game time, it will be in the first team, and I don't know if he will be involved on Monday. We will make that decision on Sunday.''