Two officers were assaulted dealing with a house party which was breaking Covid rules, Lincolnshire Police said.
Police went to the house in Allison Place, Lincoln on Saturday night and found "approximately 13" people.
The attack happened when a 21-year-old man was being arrested on suspicion of breaking lockdown restrictions.
One officer was taken to hospital with minor injuries. Police said fines were issued to a number of people attending the party.
The 21-year-old was further arrested on suspicion of assaulting police officers and was taken into custody.
Supt Lee Pache said attacks on police officers were "happening far too often".
"This latest incident is another example of how our officers are placed in the difficult position of responding to breaches of Covid legislation, which in itself brings added risks to officers in terms of risk to their health," he said.
"We'd like to remind people once again that we're still in the middle of a global pandemic, which means that we still have to comply with government guidelines.
"We all need to work together to stop the spread of the virus and to keep everyone safe, so please, play your part."
Under the new regulations that came into effect on 29 March, outdoor gatherings, including in private gardens, are permitted between two households or groups of up to six people from different households.
Mixing indoors with people outside of your household or support bubble is still prohibited.