A man was taken to hospital after falling onto the street from a residential property in the centre of Boston.
A police investigation was launched and four people were arrested.
The road was closed off for several hours after the incident, with police vehicles on the scene.
The injured man is said to be in his fifties.
The four arrested were three men, aged 34, 37 and 50, and a 64-year-old woman.
They were released under investigation yesterday.
Police are appealing for anyone with any information to contact them.
A police spokesperson said on Saturday morning: " A man in his 50’s has been injured and taken to hospital and the area is cordoned off.
Four people have been arrested and officers are keeping an open mind about what happened.
"Any witnesses should call 101 quoting incident 152 of 9 March."