A link to an illegal stream of Saturday's world heavyweight title bout between Anthony Joshua and Carlos Takam was retweeted by a police webpage.
A Twitter account belonging to Avon and Somerset Police's Operational Support Team retweeted a "spam link" on the live streaming app Periscope.
The video stream also showed pornography between rounds.
A force spokeswoman said the link appeared due to "human error" and was removed "within an hour".
In a statement, police said: "We are aware that last night a spam link, containing inappropriate content, was accidentally retweeted on one of our official A&S Police Twitter accounts.
"Unfortunately, this was due to human error and the account user was unaware that it had happened.
"The post containing the offending link was removed within an hour, as soon as we became aware of the matter.
"We would like to thank those who brought it to our attention and we apologise for any offence that may have been caused through the sharing of this content."
The spokeswoman said "appropriate precautions" would be taken to prevent a recurrence.
The fight was shown legally in the UK on Sky Sports Box Office for a fee of £19.95.
Anthony Joshua won the bout, stopping his opponent in the 10th round.