A teenage boy was arrested before this week's Merseyside Derby on suspicion of possession of a flare.
Everton and Liverpool met at Goodison Park on Wednesday for the Premier League clash, with Liverpool running out 4-1 winners.
Police said that during the match a "minority" of fans had brought pyrotechnics into the ground, and officers described the behaviour as "dangerous and reckless."
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Police said that before the match a 17-year-old boy was arrested outside Goodison.
Chief Inspector Paul Sutcliffe added an "overwhelming majority of fans" watched the game "safely and responsibly".
In a statement he said: "Merseyside Police worked extensively with both Everton and Liverpool football clubs ahead of the Merseyside derby to prevent crime and disorder and maintain public safety.
"During the game our officers were present to work with the stewards at Goodison and we were pleased that the overwhelming majority of fans watched the game safely and responsibly.
"Unfortunately, a minority of fans brought pyrotechnics into the ground which will not be tolerated by Merseyside Police under any circumstances.
"We take this dangerous and reckless behaviour extremely seriously and outside Goodison, before the match, we arrested a 17-year-old male who was in possession of a flare.
"We are working with both clubs to identify those responsible for bringing flares into the ground on Wednesday and we would urge anyone with information to please get in touch with us."
Anyone with any information can contact police via DM @MerpolCC, 'Merseyside Police Contact Centre' on Facebook or by calling 101.
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